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APR  14  1914 


The  Geology  and  Ore  Deposits  of  the  Bully 
Mining  District,  California 


V*1 
MNIVE.RSITY 

.CAILI 

BY 

ALBERT  C.  BOYLE,  JR., 

LARAMIE,  WYOMING 


SUBMITTED  IN  PARTIAL  FULFILLMENT  OF  THE  REQUIREMENTS  FOR 

THE  DEGREE  OF  DOCTOR  OF  PHILOSOPHY,  IN  THE  FACULTY 

OF  PURE  SCIENCE,  COLUMBIA  UNIVERSITY, 

DECEMBER,  1913 


CONTRIBUTIONS  FROM  THE  DEPARTMENT  OF  GEOLOGY, 
COLUMBIA  UNIVERSITY,  Vol.  26,  No.  2 


Reprinted  from  Bulletin  No.  85,  January,  1914, 
American  Institute  of  Mining  Engineers 

NEW    YORK,    N.    Y. 

1914 


TRANSACTIONS  OF  THE  AMERICAN  INSTITUTE  OF  MINING  ENGINEERS 

[SUBJECT  TO  REVISION] 

DISCUSSION  OF  THIS  PAPER  IS  INVITED.  It  should  preferably  be  presented  in  person  at  the 
New  York  meeting,  February,  1914,  when  an  abstract  of  the  paper  will  be  read.  If  this  is  impossible, 
then  discussion  in  writing  may  be  sent  to  the  Editor,  American  Institute  of  Mining  Engineers,  29  West 
39th  Street,  New  York,  N.  Y.,  for  presentation  by  the  Secretary  or  other  representative  of  its  author. 
Unless  special  arrangement  is  made,  the  discussion  of  this  paper  will  close  Apr.  1,  1914.  Any  discussion 
offered  thereafter  should  preferably  be  in  the  form  of  a  new  paper. 

The  Geology  and  Ore  Deposits  of  the  Bully  Hill  Mining  District, 

California* 

BY   A.    C.   BOYLE,    JR.,    LARAMIE,    WYO. 
(New  York  Meeting,  February,  1914) 

CONTENTS 

PAGB 

I.  INTRODUCTION, 58 

II.  LOCATION  OF  THE  DISTRICT, .60 

III.  STRATIGRAPHY, 63 

Description  of  the  Rocks, .        .63 

Triassic  Eruptives  (Andesite  Flows  and  Tuffs),    ....  63 

Triassic  Sediments  (Shales  and  Slates), 65 

Areal  Geology,    ......! 65 

Structure, 66 

Folds, .        .  66 

Faults, .69 

Shear, 70 

Intrusives, 71 

Alaskite  Dike, 71 

Andesitic  Intrusion,    .        .  ^. 72 

IV.  PETROGRAPHY  OF  THE  ROCK  TYPES, 73 

Andesite  Flows, 74 

Tuffs, 74 

Andesite  Tuff, 74 

Rhyolite  Tuff, 75 

Alaskite-Porphyry, 79 

Andesite  Dike, 81 

V.  DESCRIPTION  OF  THE  MINES, 82 

VI.  METALLIFEROUS  DEPOSITS, 85 

Character  of  the  Ores, 87 

Mineralogy  of  the  Ores, 87 

Metallic  Minerals, 87 

Microscopic  Character  of  the  Ores, 88 

Secondary  Enrichment, 93 

Genesis  of  the  Ores, 94 

VII.  THE  SULPHATE  DEPOSITS, 99 

Gypsum, .100 

Anhydrite, 100 

Barite, 100 

Origin,  with  special  reference  to  Gypsum, 101 

VIII.  SUMMARY, 103 

IX.  BIBLIOGRAPHY, 104 

*  Submitted  in  partial  fulfillment  of  the  requirements  for  the  degree  of  Doctor  of 
Philosophy,  in  the  Faculty  of  Pure  Science,  Columbia  University,  December,  1913. 


282310 


58  BULLY   HILL   MINING   DISTRICT,    CALIFORNIA 

I.  INTRODUCTION 

THE  geological  field  work  of  the  Bully  Hill  district,  upon  which  this 
paper  is  based,  was  begun  July  1,  1908,  and  covered  a  period  of  three 
months.  The  time  was  found  too  short  for  a  complete  report  and  the 
district  was  again  visited  in  the  early  part  of  July,  1912,  from  which  time 
detailed  study  of  the  locality  continued  until  September  of  the  same  year. 
This  paper  is  the  result  of  observations  made  in  the  mines  in  the  immediate 
vicinity  of  Winthrop,  Shasta  county,  CaL,  during  these  two  periods  of 
study. 

The  preparation  of  this  report  has  been  greatly  facilitated  by  various 
courtesies  rendered  the  writer  by  D.  M.  Riordan,  President  of  the  Bully 
Hill  Copper  Mining  &  Smelting  Co.,  and  by  John  B.  Keating  and  Herbert 
R.  Hanley,  managing  officers  actively  in  charge  at  the  mines.  The 
elaboration  and  further  study  of  the  notes  and  collections  were  carried  on 
in  the  laboratories  of  the  Departments  of  Geology  and  Mining  at  Colum- 
bia University,  and  the  writer  takes  pleasure  also  at  this  point  in  express- 
ing his  acknowledgments  to  Profs.  James  F.  Kemp,  A.  W.  Grabau, 
Charles  P.  Berkey,  and  William  Campbell,  for  advice  and  assistance. 

In  order  that  one  may  appreciate  at  first  reading  the  significance  of 
some  of  the  details  which  follow,  and  for  the  sake  of  clearness,  a  brief 
outline  of  the  geological  relationships  is  here  given,  together  with  certain 
conclusions  which  have  been  reached  regarding  the  genesis  of  the  ores  and 
the  gypsum  masses. 

In  the  Bully  Hill  mining  district  an  associated  series  of  Triassic  lavas 
and  tuffs,  chiefly  andesites,  is  preceded  as  well  as  followed'  by  sediments. 
The  entire  system  is  tilted  so  that  the  original  bedding  planes  dip  in 
general  to  the  southeast.  The  surrounding  region  has  been  greatly  dis- 
turbed, and  in  the  immediate  vicinity  of  the  mines  close  folding  of  the 
later  sediments  and  extreme  shearing  of  the  igneous  rocks  locally  is  a 
striking  feature. 

Into  the  nearly  vertical  shear  zones  have  been  intruded  post-Triassic 
dikes  of  various  rock  types  in  the  following  order:  alaskite-porphyry  and 
andesite-porphyry.  Outside  the  area  under  consideration  diorite  dikes 
are  known,  but  they  will  not  receive  attention  further  than  to  note  that 
they  probably  represent  a  differentiation  product  of  the  same  magma 
from  which  the  other  two  dikes  came.  In  this  connection  all  the  dikes 
have  an  important  bearing  on  the  origin  of  the  ores  and  of  the  gypsum 
found  in  the  mines. 

The  intrusion  of  the  alaskite-porphyry  as  well  as  the  later  andesite 
was  accompanied  by  the  emission  of  magmatic  waters  and  metal-bearing 
solutions.  As  these  solutions  passed  upward  they  wrought  important 
changes  in  the  rocks  within  their  influence,  and  were  directly  responsible 
for  the  introduction  of  the  various  ore  minerals,  as  well  as  some  of  the 


findesite  Flows        States.  flfasktteOite       fJndesitcDike 

and  tuffs.  and  shales. 


Limestone         7l/ffs  Shales        ftlaskiteOike.         Andes/ft. Flows        /?Mes/teffMe.         Stares  Shafts. 


FIG.  1. — MAP  OF  BULLY  HILL  MINING  DISTRICT,  WITH  GENERALIZED  SECTION   ON 

LINE  A-B. 
The  lower  structural  section  is  below  sea  level  and  involves  the  McCloud  Limestone. 


60  BULLY    HILL    MINING    DISTRICT,    CALIFORNIA 

gangue.  By  secondary  changes  which  involved  alteration,  the  ores  be- 
came enriched  so  that  in  some  cases  a  copper  content  of  8  per  cent,  was 
produced. 

Of  considerable  interest  in  this  district  are  the  relationships  between 
the  shear  zones  and  the  various  dikes;  the  shape,  extent,  and  genesis  of 
the  ore  bodies;  the  occurrence  of  large  masses  of  sulphate  of  lime,  which 
suggests  formation  by  a  process  not  heretofore  recognized  of  great  impor- 
tance. Of  great  economic  significance  are  the  association  of  copper  ores 
with  the  alaskite-porphyry,  and  the  interpretation  of  some  facts  estab- 
lished in  prospecting  the  extensive  masses  of  gypsum. 

The  area  covered  by  the  map,  Fig.  1,  extends  2  miles  east  and  west 
and  3  miles  north  and  south.  It  is  embraced  in  the  Redding  Folio  of  the 
U.  S.  Geological  Survey,  which  was  prepared  by  J.  S.  Diller,  to  whose 
careful  observations  the  writer  is  deeply  indebted.  The  recent  develop- 
ment of  the  mines  has  naturally  revealed,  however,  some  points  of  interest 
which  were  not  accessible  when  Mr.  Diller's  observations  were  made,  and 
as  a  result  some  modification  of  his  views  will  be  supported. 

II.  LOCATION  OF  THE  DISTRICT 

The  Bully  Hill  district  is  one  of  several  mineral  belts  situated  in  a 
moderately  elevated  area  in  the  western  central  part  of  Shasta  county, 
Cal.  This  county  lies  at  the  extreme  northern  end  of  the  Great  Valley  of 
California  and  embraces  a  range  of  mountains  which  is  chiefly  formed  by 
the  northward  convergence  of  two  important  mountain  chains,  the  Sierra 
Nevada  on  the  east,  which  has  a  general  north  and  south  trend,  and  the 
Coast  Range  on  the  west,  which  has  a  decided  northeast  trend.  The 
actual  junction  consists  of  short  irregular  ranges. 

The  section  of  the  country  is  roughly  in  the  shape  of  a  flat-lying  U 
with  the  opening  to  the  south.  The  Coast  Range  and  the  Sierras  form 
the  limbs,  while  the  high  slope  of  the  Sierras,  bearing  westward,  rapidly 
merges  with  the  eastern  slope  of  the  Coast  Range  and  produces  the  gentle 
curve  of  the  U  at  the  north. 

Irregular  east  and  west  ridges  parallel  to  the  curve  of  the  U  succeed 
one  another  to  the  north,  and  present  a  relatively  steep  front  to  the  south. 
The  Southern  Pacific  railway,  connecting  Sacramento  with  Portland, 
passes  up  the  Great  Valley  and  crosses  this  range  by  following  along  the 
course  of  the  Sacramento  river  and  its  tributaries.  At  a  distance  of  10 
miles  north  of  Redding  it  passes  through  the  station  of  Pit,  from  which 
the  Sacramento  Valley  &  Eastern  railway  extends  to  the  east  15  miles 
so  as  to  tap  the  copper  belt  at  Copper  City.  The  branch  finally  ends 
3  miles  farther  to  the  north  at  the  Bully  Hill  mine,  near  the  town  of 
Winthrop. 

The  productive  area  which  has  attracted  attention  for  the  past  13 


BULLY   HILL   MINING   DISTRICT,    CALIFORNIA  61 

years  and  which  is  now  under  consideration  lies  in  the  immediate  vicinity 
of  the  town.  There  are  three  local  mining  centers,  designated  as  Bully 
hill  to  the  north,  Copper  City  to  the  south,  and  the  Rising  Star  between 
these,  but  somewhat  nearer  to  Bully  Hill. 

History  of  the  Mining  Development 

The  existence  of  copper  ores  in  this  part  of  the  mineral  belt  was  known 
in  the  first  decade  of  the  '50's.  It  was  encountered  in  small  quantities 
in  tunnels  which  were  opened  primarily  for  the  gold  and  silver  veins 
which  yielded  the  placer  values.  In  1853  placer  gold  was  discovered  in 
the  vicinity  of  Bully  Hill1  and  in  1862  gold  was  found  in  the  altered  surface 
rock  near  the  present  site  of  Copper  City.2  The  copper  deposits  were 
neglected  for  the  time  being,  and  little  of  importance  happened  before 
1895. 

Oxidized  ores  from  the  surface  soon  failed  to  yield  acceptable  returns, 
and  tunneling  was  employed  with  the  hope  of  discovering  sources  which 
presumably  supplied  surface  values.  Tunnel  No.  1,  on  the  east  slope  of 
Bully  Hill  about  500  ft.  from  the  top,  was  driven  a  short  distance.  Since 
the  surface  somewhat  to  the  west  and  north  had  yielded  profitable  returns 
in  gold  and  silver,  this  tunnel  was  driven  with  the  view  of  striking  the 
gold-bearing  rock  in  depth.  As  the  working  face  advanced,  the  gossan 
which  had  yielded  the  values  changed  into  very  base  ore.  This  condition 
of  affairs  so  discouraged  the  operators  that  in  a  comparatively  short  time 
their  workings  were  abandoned,  as  it  was  the  general  belief  that  such  base 
ores  could  not  be  reduced  successfully. 

About  this  time  Iron  Mountain,  some  20  miles  to  the  southwest,  was 
located  as  an  iron  mine  by  William  Magee  and  Charles  Camden.  The 
surface  rocks  throughout  the  entire  country  were  more  or  less  stained  by 
iron  oxide;  the  gossan  was  thick  and  usually  carried  gold  values.  Practi- 
cally the  same  gossan  occurred  at  the  abandoned  claims  on  Bully  Hill. 
Since  sufficient  time  had  elapsed  for  the  timbering  in  Tunnel  No.  1  of 
Bully  Hill  to  rot,  the  property  was  relocated  and  later  passed  into  the 
possession  of  Alvin  Potter,  in  1877.  The  tunnel  was  reopened  and  re- 
timbered.  Some  ore  was  taken  out,  but  it  exhibited  such  a  base  character 
that  active  work  was  discontinued,  and  subsequently  the  property  passed 
into  the  hands  of  the  Extra  Mining  Co. 

It  now  appeared  for  the  first  time  that  the  enterprise  was  on  a  firm 
basis,  and  in  1877  the  first  ore-dressing  mill  in  Shasta  county  was  erected 
near  the  present  site  of  Copper  City  by  C.  M.  Peck.  The  mill  was  erected 
on  the  west  bank  of  Squaw  creek  and  was  known  as  the  Northern  Light 
mill. 

1  Bulletin  No.  23,  California  State  Mining  Bureau,  p.  32  (1902). 

2  Idem,  p.  33. 


62  BULLY    HILL   MINING    DISTRICT,    CALIFORNIA 

It  is  reported  that  in  three  years  the  company  extracted  nearly 
$650,000  from  the  ores.  The  rich  values  soon  began  to  decrease  or  change 
in  character  to  such  an  extent  that  this  mill  was  abandoned  after  a  com- 
paratively short  period  of  operation.  The  equipment  became  the  prop- 
erty of  Messrs.  Potter  and  Hall,  who  had  purchased  some  of  the  adjoining 
claims,  but,  like  the  Extra  Mining  Co.,  they  were  forced  to  discontinue 
operations  because  of  the  complex  nature  of  the  ores. 

The  entire  milling  industry  was  established  on  the  basis  of  returns 
from  a  250-ton  shipment  of  local  ore  sent  to  Swansea  in  1863.  It  is 
reported  that  the  ore  assayed  8  per  cent,  in  copper,  and  showed  a  value 
of  $40  in  gold  and  $20  in  silver  to  the  ton.  The  copper  content  was 
considered  of  no  value. 

In  1879  James  Salee  passed  through  this  section  of  the  country  and 
incidentally  visited  Iron  Mountain.  He  was  a  miner  of  wide  experience, 
and  in  samples  of  the  gossan  which  he  had  collected  he  found  gold  and 
silver  values.  He  became  the  sole  owner  of  the  property  at  Bully  Hill. 
Years  passed  and  occasionally  new  finds  would  be  reported,  which  boomed 
the  Copper  City  district  and  gave  a  new  impetus  to  speculation.  Little 
was  done,  however,  until  the  latter  part  of  the  '90?s,  when  the  property  was 
transferred  to  the  Bully  Hill  Mining  &  Smelting  Co.  Such  is,Jn  part, 
some  of  the  early  history  of  the  camp. 

Topography 

The  district  shown  on  the  map,  Fig.  1,  is  embraced  by  the  Klamath 
mountains  and  shows  a  well-dissected  portion  of  the  Klamath  plateau. 
The  elements  of  relief  are  not  many  and  are  easily  distinguished.  Topo- 
graphically the  most  important  feature  of  this  region  is  a  ridge  of  igneous 
rock  formed  by  the  upturned  edges  of  surface  flows  of  andesites  and  inti- 
mately associated  tuffs.  This  complex  has  been  metamorphosed  to  such 
an  extent  that  it  resists  erosion  to  a  greater  degree  than  the  limestones  to 
the  northwest,  on  which  it  rests,  and  than  the  shales  and  tuffs  which 
flank  it  on  the  south  and  east.  This  ridge  is  continuous  outside  the  limits 
of  the  map  for  a  distance  of  30  miles  and  has  approximately  a  north  and 
south  direction. 

In  general,  the  drainage  of  the  district  is  to  the  southwest  until  the 
Sacramento  river  is  reached,  after  which  it  is  entirely  south.  To  the  east 
of  the  ridge  is  Squaw  creek,  which  flows  southwesterly  and  joins  Pit 
river  near  the  southern  border  of  the  map.  The  west  slope  of  the  ridge 
is  drained  entirely  into  the  McCloud  river.  This  ridge  is  traversed  by  a 
series  of  narrow  and  steep  gulches  separated  by  steep  ridges  of  a  minor 
order. 

Bully  Hill  may  be  regarded  as  an  elevation  of  secondary  importance, 
scarcely  more  than  2,000  ft.  in  height.  The  elevations  decrease  pro- 


BULLY   HILL   MINING   DISTRICT,    CALIFORNIA  63 

gressively  toward  the  southern  limits  of  the  map.  The  topography  is 
intimately  related  to  the  general  geological  structure  of  the  district  and 
results  from  differential  erosion  of  the  various  rock  formations. 

The  lower  portions  of  the  larger  gulches  have  been  partly  filled  with 
detritus  from  the  higher  slopes,  and  in  many  parts  of  the  district  these 
have  been  worked  as  placers. 

III.     STRATIGRAPHY 

It  is  not  the  purpose  of  this  paper  to  enter  into  an  elaborate  detailed 
discussion  of  the  stratigraphy  of  the  region,  for  it  has  received  great  care 
and  special  attention  from  J.  S.  Diller,3  J.  P.  Smith,4  and  H.  W.  Fairbanks.5 
In  order,  however,  that  the  geological  relations  of  the  eruptive  rocks  and 
the  ore  bodies  may  be  fully  comprehended,  a  brief  outline  of  the  separate 
formations  is  here  introduced.  (See  Fig.  2.) 

The  oldest  rocks  in  the  Bully  Hill  district  which  outcrop  on  the  sur- 
face consist  of  a  series  of  volcanics,  everywhere  tilted  at  a  high  angle 
decidedly  to  the  southeast,  although  locally  beds  may  vary  so  as  to  be 
nearly  flat. 

This  series  consists  of  alternate  flows  and  tuffs  which  together  meas- 
ure roughly  1,500  ft.,  and  has  been  named  by  Diller6  Dekkas  andesite. 
Above  this  and  apparently  conformable  are  the  crumpled  massive  to  thin- 
bedded  shales  of  the  Pit  series.  Only  the  lower  part  of  fully  2,000  ft.  of  the 
Pit  shales  is  embraced  by  the  eastern  boundary  of  the  map. 

Description  of  the  Rocks 

Triassic  Lavas  and  Tuffs. — Andesite  flows  and  related  tuffaceous  beds, 
now  greatly  metamorphosed,  are  seen  to  cover  most  of  the  western  part 
of  the  area  under  consideration.  The  shape  and  areal  distribution  are 
shown  on  the  map,  Fig.  1.  It  is  a  matter  of  some  difficulty,  however,  to 
fix  the  precise  divisional  planes  that  separate  the  earlier  from  the  later 
flows.  This  comes  about  from  the  fact  that  one  grades  into  the  other. 
In  many  instances  the  flows  succeed  each  other  with  apparent  regularity, 
and  at  times  were  followed  by  accumulations  of  tuffaceous  materials. 
The  present  metamorphosed  condition  of  the  tuff  beds  and  the  flows  makes 
it  difficult  in  the  hand  specimen  to  draw  definite  divisional  planes.  From 
the  manner  in  which  this  andesite  series  weathers  it  is  possible  to  describe 
two  different  varieties,  but  because  of  limited  space  the  andesites  collect- 
ively will  be  described  as  a  single  unit. 

3  Redding  Folio,  No.  138,  U.  S.  Geological  Survey  (1906). 

4  The  Metamorphic  Series  of  Shasta  County,  California,  Journal  of  Geology,  vol. 
ii,  No.  6,  p.  588  (Sept.-Oct.,  1894). 

6  Geology  and  Mineralogy  of  Shasta  County,  Eleventh  Report  of  the  California 
State  Mineralogist,  p.  24  (1892). 

8  Redding  Folio,  No.  138,  U.  S.  Geological  Survey,  p.  7  (1906). 


64 


BULLY   HILL   MINING    DISTRICT,    CALIFORNIA 


The  freshest  specimens  are  dark  gray,  with  numerous  small  glistening 
phenocrysts  of  labradorite,  showing  best  on  fractured  surfaces.  The  rock 
exhibits  a  greenish  tinge,  due  to  the  presence  of  chlorite,  epidote,  and 
similar  secondary  minerals  derived  from  pyroxenes  (probably  augite). 
On  alteration  the  rock  usually  becomes  lighter  colored,  and  in  many  places 
on  first  sight  resembles  rhyolite.  Occasionally  sparsely  scattered  vesicles 
which  have  been  filled  with  calcite  occur,  and  the  presence  of  these  gives 


Triassic. 


Black  and  grayg 
shale,  with  thin 
bedded  sandstones 
f a  n  d  interbedded 
tuff.j 


Triassic. 


Andesite  fl  o  w  s 
:  and  tuffs  with  some 
rhyolite  tuff.    More 
or  less  altered. 


Tuffaceous  shale 
„  ,       .      i  with  some  sand- 

Pennsylvaman.  stones  and  lime- 
stones. 


Massive    gray 
Pennsylvanian.  limestone  carrying 
some  fossils. 


flnde&ite. 
and. 

Tuff 
1500' 


FIG.  2. — GENERALIZED  COLUMNAR  SECTION  IN  BULLY  HILL    DISTRICT,   SHOWING 

THE  INTRUSIONS. 

to  the  rock  mass  a  mottled  appearance.  Where  the  rock  is  found  thor- 
oughly altered  it  is  characterized  by  a  red  stain  derived  from  iron-bearing 
silicates.  The  secondary  minerals  are  sericite,  quartz,  kaolin  in  large 
amount,  and  minor  quantities  of  calcite  and  iron  oxide.  The  alteration 
is  often  attended  by  leaching  by  which  the  rock  changes  to  a  nearly  white 
mass,  roughly  schistose. 

In  the  valleys  where  this  andesitic  material  has  accumulated  character- 
istic red  gravelly  soil  results,  which  because  of  the  red  color  makes  it 


BULLY   HILL   MINING    DISTRICT,    CALIFORNIA  65 

impossible  to  trace  the  series  where  the  outcrops  are  obscured.  The 
massive  character  of  some  of  the  flows  is  evidenced  from  the  presence  of 
numerous  large  rounded  boulders,  which  are  to  be  seen  in  the  gulches  as 
placer  gravels. 

Triassic  Sediments. — The  Pit  Shales. — The  youngest  formation  in  the 
district  with  which  this  paper  is  immediately  concerned  is  an  extensive 
series  of  shales,  interbedded  occasionally  with  various  volcanic  tuffs.  In 
general  these  shales  are  fine-grained,  dark  gray  to  black,  characteristically 
thin-bedded,  and  frequently  provided  with  remains  of  minute  marine 
organisms. 

This  terrane  is  by  far  the  most  extensively  developed  of  any  formation 
in  the  district  and  covers  the  entire  area  of  the  eastern  part  of  the  map. 
These  shales  underlie  a  limestone  having  an  abundant  and  well-preserved 
fauna  which  is  known  to  be  Middle  or  Upper  Triassic.7  Because  of  this 
relationship  the  age  of  the  shales  is  placed  in  Middle  Triassic. 

The  average  strike  is  north  and  south  when  large  areas  are  considered, 
but  on  the  map  it  will  be  noted  that  the  strike  varies.  The  dip  is  decid- 
edly to  the  southeast,  in  common  with  the  previous  series,  and  in  amount 
it  is  not  far  from  28°.  Variable  dips  are  encountered  in  the  southeastern 
part  of  the  map. 

Where  the  shales  exist  the  topography  is  well  rounded,  and  usually  low 
lands  result.  This  is  not  because  the  series  is  characteristically  soft,  for 
there  are  some  members  making  up  the  deposit  which  are  hard  and  resist- 
ant; but  because  a  few  soft  layers  or  beds  exist.  These  are  usually  tuffs, 
and  as  they  are  washed  away  the  harder  parts,  because  of  insufficient 
support,  break  away  and  the  entire  formation  is  thus  weakened  and  the 
topography  is  thereby  subdued. 

The  rock  types  include  brownish  red  to  yellowish  red  shales  and  tuffs. 
The  shales  alter  to  lighter  shades,  browns  and  grays  predominating.  Be- 
cause of  folding  the  entire  formation  is  jointed  and  shattered,  and  over- 
turned folds  are  not  uncommon. 

Areal  Geology 

The  area  mapped  consists  of  Triassic  rocks,  which  can  be  deciphered 
into  several  distinct  types.  Along  the  southern  and  eastern  border  of  the 
map  are  found  sediments,  chief  of  which  are  shales,  sandstones,  and  inter- 
bedded  tuffs.  The  area  embraced  shows  only  a  small  part  of  a  wide- 
spread series  which  extends  north  and  south  for  many  miles,  and  stretches 
over  a  distance  of  10  miles  or  more  in  width  to  the  south.  The  western 
border  of  the  area  is  rather  irregular,  a  condition  produced  in  part  by 
stream  cutting,  but  largely  by  complex  folding  and  erosion. 

West  of  the  sedimentary  portion  is  an  extensive  area  of  igneous  rocks 


Professional  Paper  No.  40,  U.  S.  Geological  Survey,  p.  16  (1905). 


66  BULLY    HILL    MINING    DISTRICT,    CALIFORNIA 

comprising  andesites  and  andesitic  tuffs.  These  rocks  cover  the  entire 
west  half  of  the  area  under  consideration.  Irregular  masses  and  long 
strips  extend  south  and  east  from  the  main  area.  The  entire  area  has  been 
sheared  so  that  the  rocks  are  usually  of  a  pronounced  and  thinly  foliated 
type.  Into  the  sheared  country  rock  have  entered  dikes,  which  tend  to 
complicate  the  structure.  Natural  outcrops  are  abundant  and  form 
sharp  ridges,  persistent  for  long  distances.  The  hilly  tract  containing  the 
mines  embraces  this  igneous  complex  and  has  abundant  evidences  of 
mineralization.  The  ledges  of  altered  andesite  and  dikes  rise  many  feet 
above  the  general  profile,  and  obviously  present  what  physiographers  term 
a  "young"  topography.  The  rocks  over  wide  areas  are  greatly  decom- 
posed, and,  except  where  exposed  as  already  described,  have  weathered  to 
a  mantle  of  soft,  reddish  brown,  chalky  debris;  and  again  they  have  be- 
come so  thoroughly  silicified  that  their  original  character  is  entirely 
obliterated.  The  extent  and  general  areal  relationships  are  given  on  the 
map,  Fig.  1. 

Structure 

The  rock  formations,  which  have  a  general  southeasterly  dip,  are 
complicated  by  folds,  faults,  shear  planes,  igneous  intrusions,  and  meta- 
morphism  to  such  an  extent  that  in  the  immediate  vicinity  of  the  mines 
these  secondary  features  are  of  more  importance,  in  the  solution  of  the 
problems  later  discussed,  than  the  rock  types  in  which  they  are  so  con- 
spicuously found. 

In  order  that  the  significance  of  these  relations  may  be  fully  compre- 
hended, and  also  that  the  reader  may  have  at  the  outset  a  working  knowl- 
edge of  the  local  features,  it  becomes  necessary  particularly  to  appreciate 
the  character  of  the  various  metamorphic  processes  involved.  There  is  a 
very  intimate  relation  between  all  these  elements  and  the  origin  of  the 
ore  deposits.  No  single  feature  when  taken  by  itself  explains  the  situa- 
tion, but  when  all  are  taken  together,  in  proper  sequence,  they  are  directly 
responsible  for  all  the  facts  observed  with  regard  to  the  ore  genesis.  For 
convenience  and  emphasis  these  will  be  discussed  separately. 

Folds. — The  best  preserved  folds  are  to  be  seen  in  the  sedimentary 
rocks  which  flank  Bully  hill  on  the  south  and  east.  In  these  rocks  the 
compressive  forces  have  produced  a  great  variety  of  folds,  ranging  from 
those  in  which  the  flexure  is  just  perceptible  to  those  where  overturning  is 
pronounced.  The  folds  are  complicated,  variable,  and  at  times  very 
obscure.  The  simplest  type,  Fig.  3,  is  found  in  the  south  and  east  part  of 
the  area,  and  the  folds  become  progressively  more  complicated  north  and 
west  until  at  the  contact  with  the  igneous  rocks  they  are  apparently  lost 
by  grading  into  another  structure  later  to  be  discussed. 

The  prominent  phase  of  deformation  especially  noticed  in  the  vicinity 


BULLY    HILL    MINING    DISTRICT,    CALIFORNIA  67 


FIG.  3. — OPEN  FOLDING  IN  THE  PIT  SHALES. 


FIG.  4. — CLOSE  FOLDING  IN  THE  PIT  SHALES. 


68 


BULLY   HILL   MINING   DISTRICT,    CALIFORNIA 


of  the  mines  is  that  which  follows  from  compression.  Within  this  zone 
the  strata  have  shortened  and  the  greater  length  of  the  various  beds, 
previously  listed  and  described,  has  been  taken  up  by  folding.  The  bend- 
ing became  complex  and  later  reached  a  condition  in  which  the  units 
yielded  easier  to  the  applied  stresses  by  breaking  than  by  further  crum- 
pling. As  a  result,  in  the  western  part  of  the  Pit  shales,  the  adjustment  is 
characterized  by  numerous  breaks  in  the  strata.  Since  the  strata  of  the 
Pit  formation  consist  of  shales,  sandstones,  and  limestones,  there  is 
reason  to  suspect  widely  differing  structures. 

The  composition  and  thickness  of  the  various  beds  determined  in  a 
large  way  the  behavior  of  the  series  under  the  applied  stresses.  The  units 
varied  greatly  in  thickness,  and  as  a  rule  the  thicker  portions  yielded  by 
breaking  rather  than  by  bending.  On  the  other  hand,  where  the  strata 
were  thin  and  the  composition  favorable,  complex  folding  and  contortion 
resulted.  These  finally  became  more  pronounced  and  were  later  replaced 
by  thrust  and  dislocation. 

Everywhere  the  Pit  shales  are  folded,  and  so  prominent  is  this  feature 
that  the  formation  can  be  detected  for  great  distances.  These  strata 
were  not  originally  deposited  in  this  position,  but  have  been  subsequently 
deformed  by  lateral  thrusts  which  crumpled  the  units  and  caused  the 
folds.  As  might  be  expected,  folds  occur  of  every  degree  of  complexity. 
Some  are  broad  and  open,  others  are  narrow  and  compressed;  in  some 
the  strata  are  but  slightly  disturbed,  in  others  the  beds  are  actually 
twisted,  contorted  and  confused  in  the  most  extraordinary  manner. 
(See  Fig.  4.) 

The  whole  process  is  not  difficult  to  imagine,  and  it  is  furthermore  an 
absolutely  necessary  step  to  follow  if  one  wishes  to  understand  the  struc- 
tural relations  in  the  mines  as  they  now  exist.  Many  of  the  local  com- 
plexities observed  in  the  working  places  are  easily  understood  and  can  be 
explained  by  a  knowledge  of  the  structures. 

It  should  be  stated  that  in  few  places  only,  in  the  field  directly  related 
to  the  mines,  are  there  good  examples  of  complex  folds  in  the  tuffs. 
This  is  not  because  these  have  in  any  way  escaped  the  deformation, 
but  chiefly  because  extreme  shearing  and  metamorphism  have  obliterated 
all  evidences  of  such  features. 

The  greater  part  of  the  hill  in  which  the  mines  are  located  consists  of  a 
series  of  interbedded  andesites,  and  associated  tuffs.  Although  there  is  a 
wide  range  between  these  products  they  show  a  common  behavior  in  the 
development  of  shear  and  foliation.  Over  the  entire  region,  of  which  the 
area  mapped  is  a  small  part,  there  is  a  likeness  in  the  results  that  argues 
similarity  of  causes  and  materials. 

The  units  varied  greatly  in  thickness  from  point  to  point  and  often  the 
tuffs  were  mixed  in  and  incorporated  with  the  flows.  The  fragmental 
volcanic  rocks  appear  to  have  been  very  abundant  and  may  even  have 


BULLY   HILL   MINING   DISTRICT,    CALIFORNIA  69 

been  predominant  in  this  particular  locality.  As  such  they  consisted 
mainly  of  fine  dust  particles,  but  there  is  evidence  also  that  large  amounts 
of  ash,  as  well  as  some  glassy  fragments,  constituted  part  of  the 
accumulations. 

The  massive  brittle  rocks  were  originally  the  flows  and  these  have  fur- 
nished the  angular  fragments  of  the  breccias,  while  the  tuffs,  because  of 
their  porous  texture,  permitted  adjustment  to  take  place  between  the 
individual  particles  without  apparent  crush.  In  extreme  zones  of  shear 
and  brecciation,  however,  all  traces  of  former  structures  have  been 
obscured,  if  not  completely  obliterated.  The  composition  and  form  of  the 
volcanic  rocks  determined  to  some  extent  their  behavior  under  the  applied 
stresses.  Since  there  is  such  an  abundance  of  folded  structures  in  the 
sedimentary  formations  on  top  of  the  igneous  rocks,  and  a  short  distance 
to  the  west  in  formations  stratigraphically  lower,  it  follows  that  these 
deformations  exist  in  some  form,  however  badly  preserved,  in  the  igneous 
rocks  as  well,  because  the  entire  series  was  subjected  to  the  same  stresses 
and  behaved  as  a  structural  unit.  Just  how  far  these  deformations  extend 
in  depth  is  a  matter  purely  conjectural,  but  it  is  believed  that  they  have 
affected  rocks  very  early  in  the  geological  column. 

As  noted  above,  the  general  structure  of  the  district  is  comparatively 
simple,  but  there  are  minor  features  which  tend  to  complicate  it.  As  a 
result  of  the  degree  of  folding,  beds  which  were  in  the  beginning  far  below 
have  been  brought  near  to  the  surface.  These  relationships  are  shown  on 
the  structural  section  taken  along  the  line  A-B,  Fig.  1.  Actual  measure- 
ments at  depth  could  not  be  made,  but  the  surface  relationships  are  mainly 
correct.  As  will  be  seen,  the  structural  section  is  made  in  a  line  which  is 
parallel  to  the  direction  of  thrust  and  consequently  the  axes  of  the  folds 
in  the  slates  and  the  more  complex  shear  zones  in  the  igneous  rocks  trend 
northeast  and  southwest.  Furthermore,  the  axes  of  the  folds  pitch,  so 
that  the  tendency  is  for  the  ore  bodies  to  pass  into  deeper  rocks  going 
northward. 

Faults. — The  structure  of  the  district  is  affected  only  in  a  very  sub- 
ordinate way  by  faults,  but  where  these  do  occur  they  are  a  source  of 
further  complexity.  Since  the  readily  distinguishable  beds  found  in  the 
immediate  vicinity  of  the  mines  show  no  evidence  of  extensive  faulting, 
it  is  safe  to  infer  that  no  dislocation  has  taken  place  since  these  were  laid 
down.  It  is  possible,  however,  for  faults  to  have  taken  place  in  the 
earlier  rocks  and  yet  not  be  registered  in  the  sediments  within  the  area 
mapped,  but  field  study  does  not  reveal  any.  There  are  numerous  minor 
slips  and  dislocations  in  the  rocks,  but  these  are  attributed  to  shearing 
processes. 

Such  slips  have  been  encountered  in  prospecting  work,  but  they  are 
too  local  to  be  recognized  as  being  important  in  the  larger  structural 
features,  and  they  are  too  numerous  to  be  shown  on  the  map.  In  the 


70  BULLY   HILL    MINING    DISTRICT,   CALIFORNIA 

mine  workings  the  older  fractures  have  been  rehealed,  while  the  later 
cracks  are  still  open  and  furnish  circulation  channels. 

At  only  two  points  has  faulting  taken  place  on  a  scale  that  merits 
attention,  and  even  here  the  data  are  somewhat  obscure,  so  that  the 
actual  amount  of  dislocation  is  questionable.  Further  developments 
may  reveal  some  interesting  relationships.  The  shear  zones  which  stand 
up  as  silicified  ledges  on  the  hill-top  apparently  end  in  the  south  slope  of 
the  hill.  It  is  quite  possible,  however,  that  these  shear  zones  are  local; 
but  there  are  several  dikes,  which  will  receive  attention  under  "Intru- 
sives,"  which  also  outcrop  on  the  south  slope  of  the  hill,  and  these  also 
end  rather  abruptly.  After  apparent  shifting  to  the  west  about  100  ft., 
they  continue  in  their  normal  direction  southward  and  finally  disappear 
under  the  shales.  This  is  very  suggestive  of  a  fault  when  taken  in  con- 
nection with  the  dikes  and  the  shear  zones,  but  the  shales  only  a  short 
distance  to  the  east  show  no  evidence  whatever  of  any  dislocation. 

Another  possible  fault,  which  is  better  characterized  by  being  a 
"  crush  zone,"  is  seen  on  the  north  slope  of  the  hill  where  it  crosses  Town 
creek  just  northwest  of  the  main  tunnel  entrance  and  back  of  the  company 
houses.  Here  the  rocks  are  badly  brecciated  and  the  zone  is  apparently 
vertical  and  at  right  angles  to  the  foliation  planes  of  the  rock  masses  on 
each  side.  This  zone  has  been  partly  explored  in  depth  and  some  ore 
obtained.  Aside  from  these  two  instances  (and  they  are  rather  obscure) 
no  faults  of  importance  were  found  in  the  district. 

Shear. — A  structure  which  is  intimately  related  to  the  folds  and  thrusts 
is  that  of  shear.  It  may  be  regarded  as  the  limiting  phase  of  combined 
folding  and  thrusting  processes.  In  this  district  sheared  structures  are 
prominent  and  are  almost  wholly  restricted  to  the  igneous  rocks.  While 
the  massive  igneous  rocks  show  this  structure  to  some  extent,  it  is  best 
developed  in  the  tuffs,  and  in  some  of  these  it  is  so  persistent  that  the 
rock  in  places  may  be  regarded  as  typically  schistose. 

Just  as  the  shales  are  characterized  by  being  folded  rocks,  in  like 
manner  the  igneous  members  can  be  considered  as  sheared  rocks.  Just 
where  folding  ends  and  shear  begins  is  not  always  easily  determined, 
since  one  passes  by  gradual  transitions  into  the  other.  In  a  general  way 
shear  is  characterized  by  being  a  finer  structure  and  represents  a  greater 
degree  of  crush,  and  involves  changes  other  than  those  of  purely  dynamic 
character.  That  folds  and  thrusts  preceded  shear  in  the  igneous  rocks 
there  can  be  little  doubt,  but  the  persistent  type  structure  now  seen  is 
shear  alone. 

The  shear  has  developed  mainly  at  right  angle's  to  the  direction  of 
pressure  and  has  a  general  trend  corresponding  to  a  north  and  south 
plane.  In  the  district  under  consideration  the  shear  has  taken  place  on  a 
small  scale  in  all  the  rocks  and  is  widespread,  but  there  were  conditions 
which  favored  localized  shear  zones,  and  as  a  result  Bully  hill  is  char- 


BULLY   HILL   MINING    DISTRICT,    CALIFORNIA 


71 


acterized  by  three  independent  zones  which  are  approximately  parallel  to 
each  other  but  separated  by  intervals  of  several  hundred  feet.  These 
zones  are  nearly  vertical  and  have  a  north  and  south  direction.  They  are 
seen  as  irregular  ledges  which  project  above  the  general  profile  of  the  hill 
and  are  shown  in  Fig.  5.  The  material  constituting  the  rock  of  these 
ledges  is  mainly  silicified  andesite  tuffs  and  flows.  In  this  hardened  con- 
dition it  resists  the  weathering  processes  and  gives  rise  to  rugged,  steep 
slopes.  In  spite  of  the  rock  being  hard  it  splits  easily  in  a  plane  parallel 
to  the  foliation  and  is  often  characterized  by  an  abundance  of  long  parallel 
cracks  trending  north  and  south. 


FIG.  5. — LOOKING  NORTH  FROM  KILLANGER  PEAK  AT  BULLY  HILL. 
The  picture  shows  the  three  shear  zones. 

The  Intrusions 

From  observation  of  the  succession  and  character  of  the  intrusives  of 
the  district  they  present  in  their  structural  relations  one  single  type — - 
dikes,  which  are  found  well  exposed  on  the  southeast  slope  of  Bully  hill. 
They  may  be  divided  into  two  distinct  varieties,  an  earlier  acidic  (alaskite- 
porphyry),  and  a  later  one  of  andesitic  characteristics. 

Alaskite  Dike. — The  alaskite  dike,  Fig.  6,  is  found  in  detached  masses 
on  the  east  slope  of  Bully  hill  and  apparently  ends  at  the  Rising  Star 
mine,  0.75  mile  farther  to  the  south.  The  rock  is  medium  even-grained 
and  contains  a  few  small  phenocrysts  of  quartz  and  feldspar  in  a  fine-- 
grained ground  mass  of  mottled  gray  color.  The  freshest  specimens 


72 


BULLY   HILL   MINING    DISTRICT,    CALIFORNIA 


have  practically  no  dark  silicates.  Most  of  the  outcrops  exhibit  altera- 
tion and  intense  bleaching,  so  that  the  weathered,  rough,  projecting 
masses  are  colored  by  iron  oxide,  the  colors  ranging  usually  from  yellows 
through  reds  to  pinks. 

In  the  hand  specimen  the  actual  dimension  of  the  grains  is  seldom 
greater  than  5  mm.  Much  of  the  rock  is  fine-grained  and  may  be  regarded 
as  felsite-porphyry.  Of  economic  significance  are  the  nearly  vertical 
foliation  planes  and  the  cracks  along  which  ore-bearing  solutions  have 
deposited  ores  in  notable  amounts. 

The  time  of  the  intrusion  is  not  definitely  known,  but  since   the 


FIG.  6. — VIEW  SHOWING  THE  RUGGED  CHARACTER  OF  THE  ALASKITE-PORPHYRY. 


country  rock  is  believed  to  have  accumulated  in  Middle  Triassic  time,  it 
follows  that  the  intrusion  is  as  young  at  least  as  the  late  Triassic. 

Andesitic  Intrusion. — A  later  intrusive  of  decidedly  andesitic  affinities, 
mostly  decomposed  to  a  reddish  brown  exfoliated  mass,  is  exposed  on  the 
south  slope  of  Bully  hill  and  extends  in  a  more  or  less  continuous  mass  in  a 
northerly  direction  for  a  distance  of  0.75  mile.  Because  of  the  readiness 
with  which  this  dike  rock  alters,  it  is  mostly  obscured,  and  at  times  it  is 
difficult  to  distinguish  it  from  the  country  rock  through  which  it  passes. 
Were  it  not  for  the  exposures  in  ravines  and  gulches  one  would  notice 
little  difference  between  this  rock  and  the  normal  weathered  country  rock. 

The  main  body  of  the  dike  is  nearly  vertical,  irregular,  parallel  or 
nearly  so  to  the  alaskite  dike,  and  at  several  points  it  is  coincident  in 


BULLY   HILL   MINING   DISTRICT,    CALIFORNIA  73 

course  with  the  direction  of  the  main  ore  bodies.  In  the  deeper  work- 
ings of  the  mines  it  is  known  to  have  a  thickness  of  approximately  300  ft. 
To  the  south  of  the  Rising  Star  mine  it  pitches  under  the  shales  and 
disappears. 

In  the  hand  specimen  it  is  greenish  to  grayish  in  color  and  is  usually 
very  fine-grained,  although  at  times  it  is  coarse  enough  to  show  distinct 
phenocrysts.  It  frequently  exhibits  amygdaloidal  structure.  The  cav- 
ities in  all  cases  are  filled  with  calcite. 

In  common  with  the  alaskite  this  dike  sends  off  branches  which 
undergound  give  considerable  trouble  and  annoyance  in  mining  opera- 
tions. Some  of  the  smaller  branches  are  finely  felsitic  in  texture. 

The  dike  has  been  changed  by  shearing  and  alteration,  so  that  in  the 
mines  the  dike  material  exactly  resembles  sheared  masses  of  ore.  With 
reference  to  the  age  of  this  intrusion,  it  is  the  youngest  igneous  outbreak 
found  in  the  district  mapped,  and  although  a  definite  age  cannot  be 
assigned  to  it,  it  is  known  to  intersect  the  lower  members  of  the  Pit  shales 
and  therefore  must  be  as  young  at  least  as  the  series,  which  is  considered 
as  Upper  Triassic. 

IV.  PETROGRAPHY  OF  THE  ROCK  TYPES 

The  chief  object  of  the  microscopic  study  of  the  rock  types  has  been 
to  identify  them  and  to  suggest  processes  directly  connected  with  the 
genesis  of  the  deposits.  Although  the  metamorphism  is  complex  and  the 
processes  of  mineralization  have  persistently  overlapped  other  stages,  it 
is  believed  that  the  best  results  will  be  obtained  by  attempting,  as  far  as 
possible,  to  treat  the  various  stages  as  individual  and  separate  phases 
even  though  the  several  processes  have  been  simultaneous. 

The  specimens  of  rock  have  been  collected  in  a  systematic  study  of  the 
Bully  Hill  district,  and  represent  quite  fully  the  range  of  types.  In  the 
set  of  rocks  which  has  been  selected  as  typical,  rnicroscopic  study  shows 
the  following:  (1)  andesites,  andesite  tuffs,  and  some  rhyolite  tuffs  among 
the  pyroclastics;  (2)  alaskite  and  andesite  as  the  representatives  of  the 
intrusives. 

Tuffs,  of  both  the  andesitic  and  the  rhyolitic  varieties,  are  the  domi- 
nant types  and  include  11  specimens  of  the  total  24.  Next  in  importance 
are  the  andesitic  flows  which  give  rise  to  the  breccias.  Then  follow  the 
intrusives,  which  can  be  grouped  into  two  main  types:  extremely  acid  and 
moderately  basic. 

The  phases  of  mineralization  may  be  listed  under  several  different 
heads;  but  this  arrangement  does  not  mean  that  the  processes  necessarily 
followed  one  another  in  definite  sequence.  Aside  from  dynamic  changes, 
a  study  of  thin  sections  shows  that  all  of  the  following  processes  have  been 
operative  in  producing  the  present  characters  in  the  rocks  and  ores. 


74  BULLY   HILL   MINING    DISTRICT,    CALIFORNIA 

They  are:  sulphatization,  carbonatization,  sulphidation,  chloritization, 
serpentinization,  and  silicification. 

Andesite  Flows 

The  andesites  range  in  texture  from  distinctly  porphyritic  to  finely 
felsitic  and  glassy  varieties.  The  characteristic  andesite  is  a  close- 
textured,  dense,  grayish  to  greenish  rock  containing  visible  phenocrysts 
of  feldspar  in  a  greenish  ground  mass.  The  representatives  of  this  class 
accumulated  as  thick  flows,  in  some  of  which  crystallization  was  well 
advanced  before  movement  ceased. 

The  felsitic  and  glassy  varieties  are  without  doubt  those  which  were 
poured  out  on  the  surface  as  thin  flows  and  sheets.  In  some  of  these  the 
escaping  gases  have  left  the  mass  porous,  but  this  feature  is  not  always 
prominent.  The  microscopic  features  show  the  porphyritic  varieties  to 
consist  of  labradorite  with  some  hornblende  in  a  felsitic  ground  mass. 
The  feldspars  are  large  and  contain  numerous  scattered  inclusions,  pre- 
sumably ilmenite.  In  the  finer-grained  varieties  the  feldspar  and  horn- 
blende wane  and  in  the  glassy  facies  these  minerals  entirely  disappear. 

Only  fragmentary  evidences  of  biotite  remain  and  in  the  highly 
altered  types  this  is  often  indicated  by  the  arrangement  of  grains  of 
magnetite. 

The  transition  of  the  porphyritic  types  to  the  finer-grained  varieties 
is  gradual  but  distinct.  The  alteration  of  the  andesites  is  a  very  salient 
•characteristic.  Aside  from  the  ordinary  weathering  to  chlorite,  kaolin, 
and  epidote,  some  sericite  was  noticed,  especially  where  the  rocks  were 
badly  crushed.  Some  of  the  larger  phenocrysts  of  feldspar  show  internal 
strain,  as  seen  in  the  wavy  extinction.  Where  the  crush  has  been  extreme 
the  phenocrysts  are  badly  broken  and  comminuted.  The  glassy  types 
show  only  irregular  areas  traversed  by  numerous  cracks  and  fissures. 
For  the  most  part  such  areas  show  advanced  devitrification,  so  that  in  the 
present  form  they  resemble  mottled  patches  with  irregular  boundaries. 
Under  the  high  power  of  the  microscope  such  areas  resolve  into  an  aggre- 
gate of  quartz  and  feldspar.  In  cases  where  devitrification  has  not 
progressed  too  far  characteristic  glassy  textures  are  still  to  be  seen. 

Tuffs 

Only  a  small  number  of  types  belong  to  this  group  and  each  is  desig- 
nated according  to  the  kind  of  lava  fragments  it  contains.  As  a  whole 
these  rocks  do  not  possess  great  petrographical  interest.  In  the  hand 
specimen  they  are  not  conspicuously  fragmental,  but  if  examined  with  a 
pocket  lens  they  will  be  found  to  contain  lighter  and  darker  colored  grains 
imbedded  in  a  gray  ground  mass.  Numerous  small  specks  of  magnetite 
are  present.  The  following  types  seem  to  deserve  mention: 

Andesite  Tuff — The  andesite  tuff  includes  all  the  rocks  composed  of 


BULLY    HILL    MINING    DISTRICT,    CALIFORNIA  75 

volcanic  detritus  which  is  clearly  andesitic  in  composition.  The  texture 
is  therefore  of  wide  range  and  includes  rocks  made  up  of  lapilli  as  well  as 
those  consisting  of  sand  and  dust.  Under  the  microscope  the  clastic 
character  of  the  rock  is  easily  recognized  and  the  mass  is  seen  to  be  com- 
posed of  intermingled  fragments  of  feldspars  and  glass.  The  andesite 
tuffs  are  badly  altered  or  decomposed  and  this  feature  renders  them  very 
difficult  to  study.  Although  the  alteration  is  well  advanced  and  the 
particles  are  very  fine,  yet  the  microscope  shows  traces  of  porosity. 
Many  of  the  fragments  still  show  evidence  of  original  glassy  texture.  The 
tuffs  alter  to  kaolin  and  sericite,  and  where  the  ferro-magnesian  minerals 
have  been  prominent  these  have  given  rise  to  considerable  amounts  of 
chlorite  and  iron  oxide. 

Rhyolite  Tuff. — In  the  essential  features  the  rhyolite  tuff  does  not 
differ  markedly  from  the  andesitic  variety  except  in  the  presence  of  quartz 
phenocrysts  imbedded  in  a  large  amount  of  dust-like  material.  This 
dust  may  have  been  in  part  glassy,  but  the  present  metamorphosed  con- 
dition of  the  products  makes  any  trustworthy  statement  of  the  original 
condition  uncertain.  The  range  in  size  of  fragments  is  variable.  Rarely 
do  the  particles  exceed  5  mm.  in  diameter  and  three-quarters  of  the  entire 
mass  is  less  than  1  mm.  in  diameter.  The  presence  of  quartz  grains 
makes  the  identification  of  the  rock  comparatively  easy.  This  rock 
involves  glassy  fragments  as  well  as  mineral  grains,  all  of  which  are  sharp, 
angular  particles,  exactly  analogous  to  volcanic  detritus.  Although  the 
macroscopic  evidence  indicating  that  the  rock  is  tuffaceous  is  strong  the 
microscopic  evidence  is  still  stronger  and  demonstrates  completely  its 
volcanic  origin.  Numerous  stringers  of  partly  devitrified  glass  are  to  be 
seen,  together  with  numerous  small  grains  of  magnetite.  Like  the  ande- 
site tuffs,  these  rocks  are  also  porous,  and  when  altered  give  rise  to  sericite 
kaolin,  and  some  leucoxene.  The  kaolin  occurs  as  irregular  earthy 
patches  and  in  some  slides  makes  up  a  large  part  of  the  rock  mass.  The 
sericite  had  its  origin  in  the  feldspars  and  usually  occurs  as  fine  aggregates. 

The  tuffs  as  a  whole  are  mineralized  and  this  phase  will  be  described 
in  detail  on  a  later  page. 

Eleven  specimens  out  of  the  24  are  fragmental  in  character  and  were 
originally  composed  entirely  of  volcanic  detritus.  They  are  the  tuffs. 
The  fragments  vary  in  size  from  3  mm.  down  to  fine  dust.  Two  specimens 
of  the  11  are  best  classified  as  andesite  tuff,  while  the  remaining  ones  are 
decidedly  rhyolitic  in  general  make-up.  Nine  of  the  11  specimens  show 
pyrite  in  varying  amounts  from  fine  sprinklings  of  dust-like  particles,  not 
exceeding  3  per  cent,  of  the  mass,  to  those  in  which  the  sulphide  runs  as 
high  as  20  per  cent,  or  more.  One  specimen  shows  blende  in  minor 
amounts.  Seven  show  the  presence  of  chlorite  and  serpentine,  while  two 
show  notable  amounts  of  carbonate.  Seven  show  the  presence  of  gypsum 
and  all  show  traces  of  silicification. 


76 


BULLY   HILL   MINING    DISTRICT,    CALIFORNIA 


Of  the  tuffs  there  is  one  specimen  that  deserves  special  comment  since 
it  shows  some  interesting  features  not  commonly  seen  in  the  rest  but  which 
are  believed  to  be  general  throughout  the  entire  class  of  tuffs.  This 
particular  feature  is  to  be  noted  when  the  sulphate  encroaches  upon  and 
entirely  replaces  the  quartz  grains,  Fig.  7.  In  the  same  section  pyrite  is 
seen  encroaching  upon  quartz  grains  and  completely  replacing  them.  It 
appears  from  these  slides  that  the  conditions  under  which  the  solutions 
existed  were  such  that  silica  was  dissolved  and  a  sulphide  as  well  as  a 


FIG.  7  — DARK  AREA  is  A  QUARTZ  GRAIN  IN  RHYOLITE  TUFF. 
The  quartz  is  being  replaced  by  gypsum,  shown  in  the  upper  right-hand  area. 
X  50  diameters. 

sulphate  was  deposited.  It  is  well  known8  that  the  solubility  of  gypsum 
decreases  with  increase  of  temperature  above  100°  C.,  and  that  silica  is 
dissolved  with  increase  of  temperature.  It  is  quite  possible  that  the 
limits  for  the  solubility  of  gypsum  were  closely  approached,  so  that  the 
sulphate  already  in  solution  was  thrown  out  and  silica  taken  up.  Clarke9 
states  that  "Hot  waters,  charged  with  sulphuric  or  hydrochloric  acid, 


8  Seidell:  Solubilities  of  Inorganic  and  Organic  Substances  (New  York,  1911). 

9  Bulletin  No.  491,  U.  S.  Geological  Survey,  p.  459  (1911). 


BULLY   HILL   MINING   DISTRICT,    CAIJIFORIJJA.  •'"-'"•-..  77 

\  »•  ^ 

attack  nearly  all  eruptive  rocks,  dissolve  nearly  all  -bases,  and  leave 
behind,  in  many  cases,  mere  skeletons  of  silica." 

Two  specimens  of  the  24  are  typical  breccias,  the  fragments  of  which 
are  angular  in  character,  greenish  in  color  and  cemented  together  with 
gypsum.  These  rocks  are  of  such  unusual  petrographic  character  that 
they  well  merit  special  description.  The  fragments,  although  originally 
sharply  angular,  are  now  conspicuously  sheared  and  at  first  sight  resemble 


SL*  . 


FIG.  8. — THIN  SECTION  OF  A  GREENISH  FRAGMENT  FOUND  IN  GYPSUM. 
The  curved  lines,  accentuated  in  part  by  the  arrangement  of  the  black  sulphide 
grains,  are  interpreted  to  be  perlitic  cracks  of  a  glassy  rock.     X  50  diameters.     Trans- 
mitted light. 


pieces  of  serpentine.     They  are  usually  very  soft  and  at  times  are  fissured 
with  carbonate  and  sulphate  of  lime. 

Scattered  through  many  of  the  other  specimens  are  greenish  areas 
which  closely  resemble  the  fragments  of  the  breccia  in  hand  specimen, 
but  a  study  of  thin  sections  shows  that  the  fragments  of  the  breccia  were 
originally  glassy.  In  spite  of  the  degree  of  shearing  that  is  in  evidence  in 
most  of  the  surrounding  rocks,  and  also  in  these  specimens  as  well,  many 


78 


BULLY    HILL    MINING    DISTRICT,    CALIFORNIA 


details  of  their  original  texture  are  preserved  with  a  sharpness  scarcely  to 
be  looked  for  in  rocks  which  have  had  such  a  history. 

It  is  generally  agreed  that  dynamic  action  is  a  powerful  agent  in 
completely  obliterating  all  such  structures,  but  in  this  instance  it  does  not 
appear  to  hold  true.  Glassy  rocks  are  known  to  be  more  easily  attacked 
than  many  others  and  are  subject  to  either  alteration  or  complete  destruc- 
tion, so  that  preservation  of  the  glassy  breccia  without  apparent  loss  of  its 
original  earmarks  and  quick-chill  characteristics  must  be  regarded  as  very 


FIG.  9.  —  SAME  SECTION  AS  FIG.  8,  BUT  UNDER  POLARIZED  LIGHT. 


interesting,  if  not  exceptional.  In  the  hand  specimen  the  rock  presents  a 
uniformly  sheared  crystalline  matrix  in  which  are  imbedded  greenish 
fragments  varying  in  size  from  an  inch  in  diameter  downward  to  micro- 
scopic dimensions.  Most  of  the  fragments  are  heavily  pyritized  and  the 
individual  grains  of  pyrite  are  conspicuously  arranged  along  curved  lines 
which  are  exactly  analogous  to  perlitic  cracks,  Figs.  8  and  9.  Many  of 
the  fragments  show  distinct  flow  lines  under  the  moderate  power  of  the 
microscope.  In  the  hand  specimen  they  often  show  how  the  fragments 
have  been  drawn  out  into  "Augen."  In  some  types  this  arrangement 


BULLY    HILL    MINING    DISTRICT,    CALIFORNIA  79 

of  the  fragments  gives  to  the  larger  rock  masses  a  distinctly  banded 
appearance. 

In  thin  section  the  greenish  grains  are  either  isotropic  or  else  they  show 
devitrification  changes.  No  chemical  analysis  of  the  greenish  fragments 
has-been  made,  but  since  they  are  closely  related  to  flow  rocks  they  are 
provisionally  classed  as  acid  glasses.  In  one  thin  section  the  greenish 
patches  show  original  porphyritic  habit.  These  areas  generally  represent 
original  glassy  rocks  and  they  are  certainly  being  replaced  by  the  gypsum. 
Stringers  and  shreds  of  such  material  are  being  encroached  upon  from  all 
sides,  and  they  remain  as  cores.  Like  the  breccia,  these  greenish  areas 
are  heavily  charged  with  sulphides,  and  the  conclusion  is  made  that  the 
same  mineralizers  which  introduced  the  sulphates  were  influential  in 
introducing  the  sulphides  as  well.  The  sulphate  was  introduced  as  a 
vein  filling,  and  this  feature  establishes  its  secondary  character.  As  in  the 
case  of  the  breccia,  these  rocks  were  originally  flows  and  are  best  regarded 
as  acid  glasses. 

One  specimen  out  of  the  entire  series  is  classed  as  a  rhyolite  flow.  It 
is  badly  sheared,  and  under  the  microscope  shows  corroded  and  embayed 
grains  of  quartz.  Secondary  carbonate  has  replaced  some  of  the  ferro- 
magnesian  minerals,  and  this  feature  gives  to  the  rock  a  mottled  appear- 
ance. There  are  a  few  patches  of  divitrified  glass  which  still  show  pro- 
nounced flowage.  There  is  no  evidence  of  introduced  sulphate  or  sul- 
phide. Small  amounts  of  secondary  silica  are  to  be  seen  in  microgranular 
patches. 

The  remaining  specimens  are  grouped  as  dikes,  and  out  of  the  total 
number  of  rock  types  there  are  eight  representatives  which  can  be  de- 
scribed under  two  types. 

Under  this  head  are  included  only  those  dikes  which  are  intimately  re- 
lated to  the  ore  deposits.  There  are  others  in  various  parts  of  the  area 
mapped,  but  they  all  have  a  striking  similarity  in  structural  relationships. 
For  convenience  they  will  be  described  in  order  of  age. 

A  laskite-Porphyry 

This  is  the  most  conspicuous  dike  rock  in  the  district.  It  is  generally 
light  colored,  very  acid,  and  is  at  times  mottled.  The  phenocrysts  01  the 
rock  consist  of  quartz  and  feldspar,  the  feldspar  generally  slightly  pre- 
dominating. The  ground  mass  is  seen  to  consist  of  a  microgranular 
mixture  of  quartz  and  feldspar.  Some  of  the  larger  phenocrysts  of  feld- 
spar, because  of  orientation,  do  not  show  the  usual  twinning.  The  chief 
accessory  minerals  are  magnetite  in  small  grains,  apatite,  and  rarely 
zircon. 

The  quartz  phenocrysts  are  embayed  and  heavily  corroded,  as  seen  in 
Fig.  10.  The  feldspars  are  altered  in  part  to  kaolin.  There  is  little  or  no 
sericite,  and  the  specimen  is  notably  free  from  mineralization.  The  rock 


80 


BULLY   HILL   MINING   DISTRICT,    CALIFORNIA 


mass  has  been  fractured  but  has  been  later  recernented  by  quartz.  The 
alteration  products  are  chlorite  and  epidote  in  small  amount,  derived  in 
all  probability  from  original  flakes  of  mica.  The  dike  varies  in  thickness 
and  on  thin  edges  it  is  relatively  fine  grained,  while  in  the  center  of  the 
larger  masses  the  texture  is  rather  coarsely  grained. 

Although  in  places  the  rock  shows  conchoidal  fracture  it  contains ^no 
glass.     Diller 10  regarded  this  rock  as  a  surface  flow  and  recorded  it  as  being 


FIG.  10. — CORRODED    PHENOCRYST    IN    ALASKITE-PORPHYRY. 
Light  area,  quartz;  dark  area,  unaltered  ground  mass.      X  50  diameters.     Crossed 
Nicols. 

older  than  the  sedimentary  formations  apparently  resting  upon  it.  From 
his  various  published  statements  regarding  these  relationships  it  mayjbe 
inferred  that  such  a  conclusion  was  not  reached  without  some  hesitation. 
Recent  study  of  the  structural  relations  in  depth  shows  that  all  such  masses 
can  best  be  regarded  as  intrusives,  and  this  idea  was  entertained  by  H.  W. 
Fairbanks.11 


10  Redding  Folio,  No.  138,  U.  8.  Geological  Survey,  p.  8  (1906). 

11  Eleventh  Report  of  the  California  State  Mineralogist,  p.  32  (1892). 


BULLY   HILL   MINING    DISTRICT,    CALIFORNIA 


81 


Andesite  Dike 

In  appearance  the  andesite  dike  is  a  dark  gray  to  greenish  fine-grained 
rock,  sometimes  showing  a  tendency  to  amygdaloidal  structure.  The 
microscope  proves  that  the  rock  consists  of  phenocrysts  of  orthoclase 
imbedded  in  a  fine-grained  ground  mass  of  lath-shaped  feldspars.  The 
chief  accessory  minerals  are  magnetite  and  rarely  rutile.  The  rock 
appears  more  basic  than  is  actually  the  case.  It  varies  in  composition 
from  point  to  point  and  shows  in  its  northernmost  outcrop  the  presence  of 
some  pyroxenes.  Like  the  alaskite  dike,  it  also  sends  off  branches  into 
the  country  rock,  and  these  are  finely  felsitic.  Both  dike  rocks  have  been 
sheared  and  have  been  replaced  in  part  by  sulphides,  sulphates,  and  car- 
bonates. Although  the  dikes  vary  from  point  to  point  the  following 
analyses  made  on  typical  specimens  of  the  freshest  material  will  give  an 
idea  of  their  chemical  character. 

Analyses  of  Alaskite-Porphyry  and  Andesite  Dike 


(A) 


(B) 


(C) 


SiO2 78.50 

A12O3 11.50 

Fe2O3 0.11 

FeO 1.82 

MgO 0.46 

CaO 0.50 

Na20 1  6.04 

K2O none 

H2Oat  105° 0.30 

H2O  above  105° 0.82 

Ti02 0.27 

P2O6 0.03 

S 0.13 

SOs .  none 

CO2 none 

MnO 0.03 

BaO none 

ZrO2 none 

Totals 100.51 


81.25 
9.03 
0.63 
0.40 
2.48 
trace 
0.25 
1.82 
1.09 
2.81 
0.08 
trace 
0.35 
none 
none 
trace 
0.05 
none 


49.85 
17.00 


,02 
.51 
.65 
,18 
4.78 
none 
2.16 
6.65 
0.97 
0.10 
0.07 
none 
none 
none 
trace 
none 


100.24 


99.94 


(A)  and  (B),  Alaskite-porphyry  dike  rock  near  Bully  Hill  mine,  rich  in  porphyritic 
quartz.  (A)  analyzed  by  George  Steiger,  (B)  by  E.  T.  Allen. 

(C),  Andesite  dike  forming  the  east  wall  of  Bully  Hill  mine.  Analyzed  by  E.  T. 
Allen.  Bulletin  No.  228,  U.  S.  Geological  Survey,  p.  210  (1904). 

The  various  specimens  of  the  andesite  dike  show  pronounced  shear 
effects  and  along  such  planes  there  is  evidence  of  introduced  carbonates 


82  BULLY    HILL    MINING    DISTRICT,    CALIFORNIA, 

and  sulphides.  The  carbonates  fill  irregular  cavities,  and  while  the  sul- 
phide is  often  found  along  the  borders  of  the  calcite  areas  it  is  not  con- 
fined to  these  alone.  The  cracks  and  fissures  are  most  heavily  mineralized, 
although  in  one  specimen  the  sulphide  appears  to  be  uniformly  scattered 
throughout  the  mass.  In  only  one  specimen  of  the  andesitic  dike  rock 
was  sulphate  found.  One  specimen  shows  introduced  copper  carbonate. 

It  is  in  the  andesite  dike  and  its  apophyses  that  the  greatest  amounts 
of  chlorite  and  serpentine  are  found.  In  all  cases  these  products  have 
been  produced  by  hydrous  alteration  from  former  ferro-magnesian  py- 
roxenes as  well  as  amphiboles. 

More  than  half  of  the  specimens  contain  ores,  which  are  confined  to  the 
tuffs.  Where  the  gypsum  is  found  it  appears  also  to  favor  the  fragmental 
rocks,  especially  the  tuffs.  In  some  of  the  specimens  all  original  struc- 
tures are  obscured  in  the  various  processes  of  sulphatization,  sulphidation, 
and  silicification.  In  a  few  there  are  satisfactory  evidences  of  original 
minerals  and  structures  that  prove  the  tuffaceous  character  of  the  original 
rock.  In  the  rhyolites  the  phenocrysts  have  resisted  alteration  where  all 
other  structures  have  been  destroyed.  In  such  cases  the  ores  are  essen- 
tially replaced  rhyolites  and  rhyolite  tuffs.  Some  of  the  specimens  show 
marked  crushing  and  these  have  been  preserved  as  breccias.  The  sul- 
phides and  the  sulphates  were  deposited  in  some  specimens  simultaneously, 
and  in  others  the  sulphides  alone  are  promiscuously  distributed  through 
the  rocks. 

V.  DESCRIPTION  OF  THE  MINES 

The  descriptions  are  presented  according  to  the  geographic  position 
of  the  three  properties  in  three  major  groups.  The  chief  producing 
mines  have  been  divided  into  the  southern,  middle,  and  northern;  and 
comprise  the  Copper  City,  the  Rising  Star,  and  the  Bully  Hill,  respectively. 
The  writer  was  permitted  personally  to  visit  each  of  the  properties,  where 
ample  opportunity  was  enjoyed  for  studying  both  surface  and  under- 
ground geology.  Under  present  conditions  such  good  opportunities  are 
not  afforded. 

The  most  southerly  of  the  properties  is  the  Copper  City.  Although 
the  first  property  to  be  extensively  worked  it  is  now  the  smallest.  The 
ore  is  more  difficult  to  treat  than  that  of  the  others.  The  mine  is  situated 
about  1,000  ft.  west  of  Zinc  creek,  and  just  south  of  Killanger  peak.  A 
tunnel  a  few  feet  above  the  level  of  Squaw  creek  has  been  driven  to  a 
distance  of  1,000  ft.  or  more  in  a  northwest  direction,  and  for  the  greater 
part  of  the  distance  it  is  in  a  contact  zone  between  shale  on  the  east  and 
alaskite  on  the  west. 

These  broad  relationships  have  been  modified,  however,  by  extensive 
fracturing  and  fissuring,  with  some  shearing,  so  that  while  the  zone  of 


BULLY   HILL   MINING   DISTRICT,    CALIFORNIA  83 

mineralization  is  somewhat  irregular,  it  is  roughly  northeast  in  direction 
and  has  a  nearly  vertical  dip.  The  shear  zone  has  been  richly  mineralized 
and  ore  shoots  of  lenticular  shape  have  resulted.  The  thickness  of  these 
bodies  varies  from  a  thin  edge  on  the  margins  to  14  ft.  or  more  near  the 
middle.  The  width  of  the  shoots  varies  from  30  to  150  ft.  The  central 
part  of  the  shoot  is  generally  the  thickest.  The  longer  axes  coincide  with 
the  general  foliation  of  the  inclosing  rocks.  Where  the  walls  have  been 
mineralized  they  have  also  been  mined,  but  in  no  instance  have  they  been 
so  productive  as  to  be  regarded  as  important  sources  of  ore. 

The  principal  ore  bodies  have  resulted  from  the  complete  replacement 
of  the  country  rock.  The  mine  is,  however,  in  the  early  stages  of  its 
development,  and  no  very  extensive  shoot  has  been  mined  out.  The  ore 
consists  of  a  mixture  of  pyrite,  bronite,  chalcopyrite,  and  an  abundance  of 
sphalerite.  There  are  also  minor  amounts  of  galena  scattered  through 
the  masses.  In  later  years  the  sphalerite  has  become  so  abundant  as  to 
make  the  extraction  of  the  copper  difficult.  The  workings  have  also 
revealed  a  badly  sheared  intrusive  dike,  containing  copper  minerals, 
apparently  not  original.  They  are  subsequently  described. 

The  next  property  is  about  2  miles  to  the  north  of  Copper  City,  and 
although  it  is  the  latest  of  all  to  be  worked,  it  is  nevertheless  of  great 
importance.  The  mine  is  called  the  Rising  Star  and  is  situated  near  the 
head  of  Buck  gulch,  which  has  its  source  in  the  south  slope  of  Bully  hill. 

The  andesites,  alaskite-porphyry,  and  andesitic  dike  are  well  exposed. 
So  far  as  known  the  andesite  dike  lies  wholly  to  the  east  of  the  principal 
ore  body,  and,  as  already  stated,  is  faulted  so  that  detached  portions  are 
shifted  to  the  west.  The  main  lodes  are  lenticular  in  shape,  with  their 
longer  axes  pitching  60°  or  more  to  the  north,  and  having  a  general  strike 
of  N.  10°  E.  The  shoots  have  been  formed  by  replacement  of  the  sheared 
rock. 

The  ores  are  mixtures  of  sulphides,  chief  of  which  are  pyrite,  chal- 
copyrite, and  bornite,  with  small  quantities  of  sphalerite.  Of  special 
interest  in  this  mine  are  masses  of  gypsum  and  anhydrite,  with  minor 
amounts  of  barite,  the  latter  being  sparingly  present  in  the  ores.  The 
workings  are  extensive  and  have  reached  a  depth  of  approximately 
1,000  ft.  The  surface  geology  presents  rocks  which  consist  almost 
entirely  of  sheared  andesites  and  tuffs  highly  stained  with  iron  oxide. 
The  andesite  dike,  although  not  conspicuous,  is  known  to  exist  to  the  north 
and  east  of  the  main  tunnel.  At  the  time  of  this  writing  no  commercial 
ore  has  been  found  east  of  the  dike. 

The  northernmost  property  comprises  the  Delamar  lode  of  Bully  Hill. 
This  mine  is  the  most  extensively  developed  of  all.  It  is  situated  on  the 
south  slope  of  Town  creek,  which  has  its  source  in  the  northeast  slope  of 
Bully  hill  and  the  southeast  slope  of  Town  mountain.  The  workings  are 
entered  by  means  of  a  tunnel,  Fig.  11,  1,400  ft.  long,  which  passes  into 


84 


BULLY   HILL   MINING   DISTRICT,    CALIFORNIA 


the  hill  in  a  general  southwest  direction.  The  shaft  near  the  end  of  the 
tunnel  is  more  than  1,000  ft.  deep  and  connects  with  a  number  of  drifts 
and  cross-cuts. 

The  geology  is  similar  to  that  of  the  Rising  Star  mine.  The  general 
structure  is  simple,  but  the  details  of  the  structure  and  the  deformation 
which  produced  it  are  not  only  complex  but  in  some  instances  are  beyond 
exact  determination.  This  is  due  to  the  complex  folding  of  the  igneous 
members. 

The  ore  bodies  are  strikingly  lenticular  in  shape  and  conform  perfectly 
to  the  foliation  of  the  sheared  country  rock.  The  lodes  lie  much  nearer 


FIG.  11. — THE  MAIN  PORTAL  OF  BULLY  HILL  MINE,  LOOKING  SOUTHWEST. 
Alaskite-porphyry  seen  immediately  above  the  right-hand  end  of  building. 

the  andesite  dike  than  those  in  the  Rising  Star  mine.  They  are  richer 
nearer  the  dike  and  leaner  as  they  are  followed  toward  the  west.  From 
detailed  study  there  is  no  doubt  that  the  shoots  represent  completely 
replaced  sheared  rock,  which  may  be  andesites,  tuffs,  or  alaskite  porphyry. 

The  lenticular  bodies  range  in  size  from  masses  a  few  inches  in  dimen- 
sions to  those  of  hundreds  of  feet  in  length.  The  thickness  appears  to  be 
controlled,  in  part  at  least,  by  the  width  of  the  more  completely  sheared, 
and  therefore  the  more  easily  replaced,  country  rock. 

Gypsum  and  anhydrite  occur  here  substantially  in  the  same  way  as  in 
the  Rising  Star  mine,  and  will  receive  discussion  under  the  topic,  "The 
Gypsum  Masses." 


BULLY   HILL   MINING   DISTRICT,   CALIFORNIA  85 

Summary. — It  is  plain  from  the  preceding  statements  that  the  mines 
are  located  in  a  line  corresponding  closely  with  the  shear  zone.  The  shoots 
are  strikingly  lenticular  in  shape,  with  their  longer  axes  parallel  to  the 
foliation  of  the  inclosing  rock  masses;  their  longer  axes  also  pitch  steeply 
to  the  north,  and  the  deposits  in  places  attain  a  thickness  of  30  ft.  or  more. 
Additional  descriptions  of  the  ore  bodies  will  be  given  under  "  Metallifer- 
ous Deposits." 

VI.  METALLIFEROUS  DEPOSITS 

The  metalliferous  deposits  of  the  Bully  Hill  district,  so  far  as  known,  are 
simple  and  uniform,  and  constitute  three  principal  tracts  intimately 
related  to  an  igneous  intrusive  (alaskite-porphyry)  locally  known  as 
Bully  Hill  quartzite.  These  tracts  are  represented  on  the  map  and 
roughly  embrace  an  area  of  1  by  3  miles: 

The  Bully  Hill  and  Rising  Star  mines  form  a  group  comprising  the 
most  important  ore  bodies  of  the  district,  and  although  ore  is  known  at 
Copper  City,  and  the  mines  have  been  operated  at  irregular  intervals  for 
many  years,  the  composition  of  the  ores  has  until  recently  made  the  mine 
of  small  importance.  Detailed  study  of  the  ore  bodies  shows  disconnected 
but  often  overlapping  masses  varying  in  size  from  mere  flattened  nodules 
several  inches  in  diameter  to  large  masses  hundreds  of  feet  in  length  and 
30  ft.  or  more  in  width. 

These  characteristically  lenticular  masses,  which  are  roughly  parallel 
to  the  andesite  dike  previously  mentioned,  and  which  lie  between  it  and 
the  alaskite-porphyry,  pitch  steeply  to  the  north  and  are  longest  in  that 
direction.  The  crushed  rock  contiguous  to  the  ore  bodies  and  wholly 
within  the  shear  zone  is  generally,  but  not  always,  impregnated  with 
sulphides.  It  follows,  therefore,  that  there  exist  in  the  mines  theoretically 
two  distinct  masses  of  ore,  one  having  a  roughly  lenticular  shape,  the 
other  somewhat  irregularly  replaced  brecciated  rock.  The  latter  is  an 
important  source  of  ores,  and  at  times  is  characterized  by  more  or  less 
complete  secondary  enrichment.  It  might  be  stated  that  while  there  are 
two  distinct  modes  of  ore  occurrence,  there  is  rarely  any  distinction 
between  the  minerals  common  to  both.  Occasionally  there  are  residuary 
cores  of  rock  in  the  ore  which  indicate  replaced  fragments.  Aside  from 
this  the  only  distinction  is  based  on  sparsely  distributed  minerals  in  the 
country  rock. 

As  the  ore  bodies  lie  wholly  within  a  metamorphosed  area  of  igneous 
rocks,  the  individual  members  of  which  have  been  sheared  and  dis- 
turbed, it  follows  that  the  shoots  themselves  may  likewise  be  disturbed. 
Careful  study  shows  that  subsequent  to  the  original  deposition  of  the 
major  ore  bodies  several  later  dynamic  movements  have  taken  place, 
each  producing  fractures  which  have  affected  the  mineral  deposits. 


86  BULLY  HILL   MINING   DISTRICT,    CALIFORNIA 

Although  the  movements  have  for  the  most  part  been  of  the  minor  order, 
the  subordinate  fracturing  has  taken  place  mainly  parallel  to  the  foliation 
of  the  country  rock.  It  is  also  believed,  upon  good  evidence  in  the  field, 
that  important  shifting  has  resulted  at  approximately  right  angles  to  the 
existing  shear  zone.  Because  of  the  number  and  character  of  the  frac- 
tures it  is  impossible  to  determine  definitely  the  ages  of  the  different 
movements. 

This  condition  is  therefore  favorable  to  the  existence  of  faulted  parts 
of  the  main  ore  body,  and  applies  especially  to  the  north  end  of  the  Dela- 
mar  lode  in  Bully  Hill.  The  evidence — though  obscured  by  the  badly 
sheared  country  rock,  and  therefore  of  rather  unsatisfactory  character — 
shows  that  in  all  probability  the  faulted  portion  can  be  looked  for  farther 
to  the  east  than  the  main  lode  in  Bully  Hill.  The  strongest  evidence 
bearing  on  such  interpretation  is  twofold:  first,  the  isolated  mass  of 
alaskite-porphyry  near  the  eastern  end  of  Bully  Hill  dump,  which  is 
thought  to  be  shifted  from  a  position  which  it  once  had  near  the  main 
tunnel,  eastwardly  to  its  present  position;  secondly,  the  brecciated  zone 
and  otherwise  ground-up  material  just  above  the  wagon  road  leading  to 
the  Rising  Star  mine  and  directly  back  of  the  company  houses  as  one  goes 
south.  This  broken  and  fractured  zone  is  axially  in  line  with  an  escarp- 
ment produced  by  an  abrupt  ending  of  alaskite-porphyry  just  west  of  the 
main  portal.  Such  brecciated  zones,  within  the  mineralized  area,  have 
received  secondary  enrichment  by  copper-bearing  solutions. 

In  a  broad  way  the  general  distribution  of  the  productive  ore  zones 
with  reference  to  the  various  rock  formations  has  been  indicated  in  a 
previous  part  of  this  paper.  In  all  cases  the  deposits  occur  in  or  in  close 
association  with  altered  igneous  rocks,  generally  alaskite-porphyry, 
which  because  of  fracture  and  partial  alteration  exhibit  various  stages  of 
replacement.  The  occurrence  of  the  ore  in  depth  is  indicated  on  the 
surface  by  a  reddish,  usually  porous,  iridescent  gossan,  and  is  coextensive 
with  it. 

When  the  ore  bodies  had  been  finally  completed,  and  when  by  dynamic 
movements  they  were  placed  above  the  level  of  ground  water,  oxidation 
resulted  and  the  subsequent  production  of  the  gossan  began.  It  is 
believed  that  a  very  great  vertical  extent  of  ore  was  in  this  manner 
affected,  and  it  is  quite  certain  that  the  solutions  which  leached  the  sur- 
face rocks  migrated  downward,  carrying  with  them  the  salts  which  they 
could  hold  in  solution,  until  they  came  in  contact  with  the  reagents  which 
would  cause  precipitation.  It  follows,  therefore,  that  the  leaner  masses 
below  would  receive  contributions  from  above  and  thus  become  enriched. 

The  vertical  distribution  of  the  ore  bodies  at  present  (1913)  is  known 
to  be  1,000  ft.,  and  at  this  depth  oxidized  minerals  exist  but  as  compared 
with  upper  levels  their  amount  is  waning.  The  downward  limit  of  the 
copper  ores  has  not  been  determined. 


BULLY   HILL   MINING    DISTRICT,    CALIFORNIA  87 

The  areal  distribution  is  shown  on  the  map,  but  because  of  the  charac- 
teristic weathering  of  the  surface  rocks,  and  the  subsequent  spreading  of 
the  gossan,  there  is  no  sharp  distinction  between  the  country  rock  and  the 
mineralized  rock.  In  very  general  terms  it  might  be  stated  that  the  Dela- 
mar  lode  can  be  traced  on  the  surface  for  a  half  mile,  and  the  Anchor 
lode  of  the  Rising  Star  mine  for  a  quarter  mile.  The  width  of  the 
mineralized  zone  varies,  but  in  round  figures  it  is  not  far  from  300 
to  500  ft. 

Character  of  the  Ores 

In  a  number  of  instances  pyrite  appears  to  be  the  chief  mineral,  with 
chalcopyrite  as  a  very  common  and  characteristic  associate.  More  rarely, 
and  chiefly  in  the  zones  where  oxidation  and  enrichment  have  been  in 
progress,  we  find  chalcocite,  bornite,  covellite,  and  native  copper.  The 
typically  oxidized  ores  if  followed  down  to  sufficient  depth  invariably 
give  way  to  secondary  enriched  products,  and,  when  these  are  not  promi- 
nent, to  the  unaltered  sulphides.  Although  some  grains  of  metallic 
copper  are  found  in  the  superficially  changed  rock,  the  decrease  in  assay 
values,  going  downward  in  the  rocks,  is  doubtless  to  be  explained  by  the 
well-known  fact  that  along  open,  water-bearing,  shear  and  fracture  zones, 
under  the  action  of  surface  waters,  copper  minerals  suffer  rapid  alteration 
and  transportation,  and  only  in  the  uppermost  parts  of  the  sheared  zone, 
especially  where  reducing  agents  have  had  play,  do  we  find  grains  of 
metallic  copper. 

At  present  the  deposits  of  commercial  value  are  mainly  those  which 
are  below  the  gossan  and  are  confined  to  that  part  of  the  zone  where 
enrichment  has  taken  place.  Wherever  the  products  of  enrichment  are 
present  chalcopyrite,  chalcocite,  covellite,  etc.,  associated  with  zinc  blende 
are  found. 

Some  shipping  ore  in  the  Bully  Hill  district  carries  as  much  as  6  per 
cent,  of  copper,  but  the  smelting  ores,  which  furnish  the  bulk  of  the  out- 
put, range  from  3  to  5  per  cent,  of  copper,  and  a  few  ounces  of  the  precious 
metals,  mostly  silver,  to  the  ton.  The  ores  of  the  various  mines,  as  well  as 
different  parts  of  the  same  mine,  exhibit  a  considerable  range  in  tenor. 
In  the  outcrop,  where  the  gossan  is  in  great  abundance,  small  nuggets  of 
gold  have  been  found.  It  is  from  this  source  chiefly  that  gold  has  been 
derived  for  the  placers. 

There  are  many  surface  outcrops  which  still  yield  gold  after  the  rock 
is  crushed  and  panned.  It  follows,  therefore,  that  the  gossan  carries 
higher  values  in  gold  than  the  ore  extracted  at  depth. 

Mineralogy  of  the  Ores 

Metallic  Minerals  (Metals). — Filaments  of  native  copper  occur  in 
greatly  altered  and  much-bleached  country  rock,  detailed  study  of  which 


88  BULLY   HILL   MINING   DISTRICT,    CALIFORNIA 

indicates  that  originally  the  masses  were  rhyolites  or  rhyolite  breccias. 
The  surface  rocks  by  early  mining  methods  yielded  notable  amounts  of 
native  copper,  but  at  present  such  materials  are  not  an  important 
source  of  the  metal.  Just  how  the  copper  accumulated  is  not  known, 
but  in  all  probability  the  presence  of  organic  compounds  played  an  im- 
portant part  in  its  reduction. 

Practically  all  the  gold  obtained  by  hydraulic  mining  occurs  in  the 
native  state.  Although  the  particles  are  uniformly  small  they  are  usually 
visible  on  close  inspection  in  all  the  detrital  accumulations. 

In  the  oxidized  ore  the  gold  occurs  in  a  siliceous,  limonitic  matrix, 
which,  without  doubt,  contributed  to  the  placers  of  local  areas.  From 
the  intimate  relation  of  the  gold  with  the  gossan  it  is  evident  that  a  very 
close  association  exists  between  it  and  the  original  sulphur-bearing  min- 
erals. In  the  pyrites,  however,  the  gold  is  in  such  a  state  of  fine  subdi- 
vision and  is  present  in  such  small  quantity  that  it  has  not  been  recognized 
under  the  microscope.  While  most  of  the  gangue  runs  high  in  iron  oxide, 
the  gold  is  frequently  closely  associated  with  cryptocrystalline  quartz. 
In  the  mine  workings,  and  particularly  in  the  vicinity  of  the  basic  dike, 
there  appears  to  be  a  genetic  relation  and  close  association  with  barite  and 
sulphides  in  which  the  gold  is  apportioned  evenly  through  the  mass.  On 
the  surface  this  mass  alters  to  limonite,  quartz,  barite,  kaolinite,  and  in  a 
few  places  to  hematite. 

Native  silver  of  delicate  filiform  and  more  solid  shapes  has  been  re- 
ported from  the  upper  levels  of  the  mine  workings.  It  is  commonly 
associated  with  the  gold  in  the  iron-stained  capping  rock,  and  occasionally 
with  minute  quantities  of  malachite  and  azurite.  The  largest  and  richest 
masses  are  found  wholly  within  the  oxidized  zone  quite  near  the  surface. 
It  decreases  with  depth  and  is  generally  accompanied  by  an  increase  in 
zinc  and  galena,  minerals  which  seriously  interfered  with  the  early  amal- 
gamation methods  adopted  at  Copper  City.  It  may  be  stated  that  in 
general  the  occurrence  of  silver  is  less  common  than  native  copper. 

Microscopic  Characters  of  the  Ores. — The  material  for  microscopic 
examination  was  collected  for  the  purpose  of  establishing  the  sequence  of 
ore  deposition.  In  order  to  study  these  problems,  a  series  of  selected 
specimens  were  polished  and  examined  by  reflected  light,  the  general 
procedure  following  that  of  the  recent  researches  of  Prof.  William  Camp- 
bell and  others. 

The  chief  opaque  minerals  of  interest  which  enter  into  the  composition 
of  the  ores  of  the  Bully  Hill  mining  district  are,  in  order  of  their  impor- 
tance, pyrite,  chalcopyrite,  blende,  bornite,  galena,  and  covellite,  with 
minor  amounts  of  chalcocite.  Not  infrequently  transparent  minerals 
also  are  present  in  the  specimens,  chief  of  which  are  quartz,  calcite,  and 
gypsum.  These  minerals,  because  of  the  close  resemblance  to  each  other 


BULLY  HILL   MINING   DISTRICT,    CALIFORNIA 


89 


when  observed  by  this  method,  are  best  identified  in  sliced  sections  rather 
than  by  reflected  light. 

Pyrite. — Detailed  studies  show  that  in  the  freshest  specimens  of 
alaskite-porphyry  there  are  no  metallic  sulphides  which  crystallized 
from  fusion  as  did  the  other  components  constituting  the  rock  mass. 
Pyrite  is  indeed  found  disseminated  through  the  alaskite,  but  it  is  believed 
that  it  was  formed  at  a  time  after  the  alaskite  had  solidified.  In  this 
occurrence  the  mineral  usually  forms  aggregates  and  grains.  Individual 
crystals  of  free  growth  and  sufficiently  large  for  recognition  of  the  crystal 


FIG.  12. — LEAN  PYRITE  ORE  WITH  VEINS  OF  CHALCOPYRITE. 
Reflected  light.     X  50  diameters. 

habit  are  comparatively  rare.  Such  faces  as  are  visible  indicate  that  the 
prevalent  form  is  the  pyritohedron,  variously  modified.  When  the  crys- 
tals have  been  able  to  grow  without  mutual  interference,  which  frequently 
happens  in  places  filled  with  soft  massive  gypsum  or  kaolinite,  the  usual 
form  assumed  is  a  sharply  defined  cube,  in  some  instances  modified  by 
octohedral  and  dodecahedral  faces.  Such  forms  have  been  noted  par- 
ticularly in  the  Delamar  lode  of  Bully  Hill.  Some  brilliant  crystals  have 
been  found  imbedded  in  a  quartzose  matrix  just  to  the  north  of  Bagster 


90 


BULLY    HILL    MINING    DISTRICT,    CALIFORNIA 


shaft.  These  studies  show  that  pyrite  was  the  first  of  the  ore  minerals  to 
crystallize.  Whether  or  not  the  pyrite  is  auriferous  is  not  easily  deter- 
mined. That  it  is  not  highly  so  is  certain,  since  tests  of  the  most  pyritous 
matter  often  show  little  or  no  gold,  and  an  abundance  of  pyrite  is  gen- 
erally a  sign  of  poor  rather  than  of  rich  ore. 

Where  the  pyrite  is  in  masses  innumerable  branching  cracks  traverse 
the  specimen  in  every  direction  (Fig.  12).  As  far  as  could  be  determined, 
no  other  metallic  mineral  of  importance  could  be  seen.  This  fact  does 


FIG.  13. — BRECCIATED  COUNTRY  ROCK. 
Filling  material  chalcopyrite.     Reflected  light.      X  50  diameters. 

not  fully  coincide  with  the  results  of  chemical  investigation,  because  it  is 
almost  impossible  to  select  any  sample  of  lean  pyrite  that  will  not  give 
traces  of  copper.  Whether  the  pyrite  contains  minute  grains  of  a  copper 
mineral  as  a  mechanical  inclusion,  or  whether  the  pyrite  is  a  lean  chemical 
compound  of  copper  and  iron,  could  not  be  determined  by  this  method  of 
reflected  light.  Aside  from  the  chemical  tests  the  pyrite  appears  to  be 
pure,  .and  its  deposition  for  convenience  has  been  designated  as  the  pyrite 
phase. 

Chalcopyrite. — The   second   stage   of   ore   deposition   is    apparently 


BULLY   HILL   MINING   DISTRICT,    CALIFORNIA  91 

characterized  by  the  introduction  of  chalcopyrite  (Fig.  13).  This 
primary  mineral  closely  followed  pyrite,  although  in  rare  instances,  as 
stated  by  L.  C.  Graton,12  "small  grains  of  chalcopyrite.  .  .  are  inclosed 
in  the  pyrite  individuals."  Studies  made  by  the  writer  point  to  the 
conclusion  that  chalcopyrite  has  been  the  last  mineral  to  enter.  This 
mineral  completely  surrounds  the  pyrite  grains  and  in  some  instances 
enters  the  minutest  fissures  of  the  partly  crushed  pyrite  masses.  At 
times  the  pyrite  and  the  chalcopyrite  are  so  inextricably  mingled  that 
their  physical  appearances  are  almost  identical,  and  it  becomes  difficult 
if  not  impossible  to  distinguish,  in  the  hand  specimen,  one  mineral  from 
the  other.  In  such  cases  simultaneous  deposition  may  be  employed  to 
explain  these  complex  relationships,  although  from  the  examination  of 
many  specimens  the  evidence  indicates  chalcopyrite  as  being  later  than 
the  pyrite. 

Sphalerite. — Like  pyrite  and  chalcopyrite,  sphalerite  is  one  of  the 
primary  minerals  and  is  everywhere  crystalline.  Sphalerite  is  later  than 
pyrite  and  is  seen  to  surround  particles  of  this  mineral.  Unlike  the  pyrite 
with  which  it  is  so  intimately  related,  it  does  not  form  well-bounded 
crystals  even  where  conditions  of  free  growth  appear  to  have  been  favor- 
able. The  blende  is  so  common  throughout  some  of  the  ores,  especially 
those  near  Copper  City,  that  a  zinc-extraction  plant  is  now  being  con- 
structed for  its  recovery.  Near  the  surface  it  is  easily  oxidized,  and, 
aside  from  a  few  occurrences,  its  products  appear  as  sulphates  on  the 
walls  of  the  mine  workings. 

Bornite. — The  isometric  sulphide  of  copper  (peacock  copper  ore, 
CusFeSi),  though  moderately  abundant  as  a  secondary  mineral,  is  very 
sparingly  found  in  the  primary  ore  of  the  district.  It  is  always  massive 
with  a  recognizable  crystalline  structure,  and  is  generally  met  in  forms 
irregularly  rounded,  closely  related  to  the  other  sulphides.  In  no  instance 
is  it  entirely  isolated,  but  according  to  microscopic  study  it  is  intimately 
associated  with  pyrite  and  chalcopyrite,  and  in  some  cases  clearly  shows 
close  association  with  sphalerite. 

Galena. — Primary  sulphide  of  lead  occurs  sparingly  in  the  copper  ores 
of  (the  Bully  Hill  district.  It  is  rarely  isolated,  but  occasionally  it  is 
found  sparsely  disseminated  through  country  rock  at  the  Bagster  shaft. 
It  occurs  in  massive  form,  both  cleavable  and  granular,  rarely  crystalline 
and  never  crystallized.  It  is  not  widespread  in  any  of  the  mines  studied 
and  is  found  intimately  associated  with  primary  chalcopyrite,  pyrite, 
and  blende.  It  has  been  noted  especially  in  the  high-grade  sulphide  ores 
of  the  Delamar  lode  (Fig.  14)  with  the  other  sulphides.  It  does  not 
occur,  so  far  as  known,  in  the  workings  of  the  Copper  City  or  Rising  Star 
mines.  Since  galena  is  rarely  encountered  in  depth  its  alteration  products 

18  Bulletin  No.  430,  U.  S.  Geological  Survey,  p.  103  (1910). 


92  BULLY   HILL    MINING   DISTRICT,    CALIFORNIA 

on  the  surface  were  not  observed.  It  is  quite  probable  that  the  galena  as 
well  as  the  blende  is  argentiferous,  and  that  would  explain  the  presence 
of  high  silver  values  in  the  gossan  as  well  as  in  the  regular  mine-run  of  ore. 
Tt  is  plain  from  a  detailed  study  of  the  relationships  of  the  minerals  that 
galena  favors  rich  sulphides,  especially  where  blende  is  in  large  amount. 
Chalcocite. — The  cuprous  sulphide  is  not  a  common  mineral  in  any  of 
the  ores  of  the  district.  It  occurs  as  dotted  masses  intimately  associated 
with  bornite.  Mr.  Graton13  states  that  chalcocite  and  bornite  apparently 


FIG.  14. — RICH  COPPER  ORE. 

White  areas,  galena;  darker,  bornite  and  chalcopyrite;  black,  quartz.     Reflected 
light.     X  50  diameters. 

take  the  place  of  chalcopyrite  as  an  irregular  network  through  and  around 
the  other  sulphides.  Chalcocite  was  found  in  small  amounts  in  the  deep- 
est workings  of  the  Bully  Hill  mine  and  has  been  regarded  by  Graton14  as 
primary  as  well  as  secondary.  From  recent  studies  made  by  the  writer, 
although  not  rigidly  limited,  it  is  generally  confined  to  the  upper  levels  in 
close  association  with  other  enriched  sulphides. 

13  Bulletin  No.  430,  U.  S.  Geological  Survey,  p.  104  (1910). 

14  Idem,  p.  105. 


BULLY   HILL   MINING   DISTRICT,    CALIFORNIA  93 

Secondary  Enrichment 

The  oxidized  zone  in  the  Bully  Hill  district  continues,  in  general,  to 
unusual  depths.  The  lower  limit  is  known  to  be  as  low  as  the  1,000-ft. 
level.  The  ore  in  this  zone  is  considerably  enriched,  and  the  enrichment 
was  materially  favored  by  the  openness  of  the  mass  because  of  the  abun- 
dance and  relative  size  of  the  cracks  and  fissures,  these  being  possible  only 
in  materials  which  are  brittle,  such  as  quartz  and  pyrite. 

The  profound  modification  resulted  chiefly  through  the  action  of 
descending  waters  which  in  their  downward  course  traversed  zones  in 
which  small  but  important  amounts  of  copper-bearing  sulphides  existed. 
The  following  equation  illustrates  the  probable  chemical  reaction: 

CuS04  +  2  FeS  =  CuFeS2  +  FeS04. 

As  an  illustration  of  the  principles  of  ore  deposition,  or,  rather,  ore 
concentration,  this  chemical  reaction  can  hardly  be  overestimated,  and 
since  the  conditions  assume  the  presence  of  copper  minerals  near  the  sur- 
face, this  phenomenon  is  usually  related  to  the  second  concentration. 
The  first  is  believed  to  have  been  brought  about  chiefly  through  the  action 
of  ascending  hot  waters,  while  the  second  concentration  is  almost  exclu- 
sively related  to  cool  descending  waters.  It  follows  from  this  that  if  the 
concentration  processes  be  regarded  as  cycles  the  first  is  far  the  more 
important,  and  as  suggested  was  directly  related  to  the  intrusion  of  the 
acidic  (alaskite)  dike.  Copper-bearing  rock  which  probably  contained 
less  than  1  per  cent,  of  copper  will  now  show  from  6  to  8  per  cent,  in  the 
oxidized  zone.  Where  the  replacement  has  been  complete  more  or  less 
calcite,  quartz,  and  barite  are  found.  It  should  be  stated,  however,  that 
while  barite  has  been  found  in  the  ores  it  is  not  at  all  important.  J.  S. 
Diller15  regards  the  barite  as  a  primary  constituent  of  the  ores.  Calcite 
and  quartz  are  wholly  secondary  and  occur  more  or  less  abundantly  at  all 
levels  of  the  various  mines. 

In  most  cases  observed  the  mineral  relations  are  fairly  definite  and 
leave  little  room  for  question.  In  other  relations  there  is  room  for  more 
than  one  inference.  The  order  given  is  believed  to  be  correct  in  the  main. 
The  disturbing  element  in  most  instances  is  alteration.  In  no  specimen 
is  there  any  suggestion  of  a  distinctive  silver  mineral,  although  the  ores 
yield  several  ounces  to  the  ton.  The  presence  of  other  sulphides,  notably 
arsenic  and  antimony,  was  not  detected.  The  enriched  sulphides  taken 
from  the  deepest  levels  of  the  mines  are  indicative  that  the  lower  limit  of 
descending  circulating  ground  water  has  not  been  reached,  and  therefore 
that  the  zone  of  lean  sulphides  has  not  been  entered. 

One  other  mineral  of  great  importance  and  intimately  associated  with 

18  Redding  Folio,  No.  138,  U.  S.  Geological  Survey,  p.  12  (1906). 


94  BULLY   HILL   MINING   DISTRICT,    CALIFORNIA 

the  ores,  especially  of  the  Bully  Hill  and  Rising  Star  mines,  is  the  hydrated 
sulphate  of  calcium,  gypsum.  L.  C.  Graton16  reports  anhydrite  as  well, 
but  so  far,  the  examination  of  many  slides  has  not  revealed  its  presence 
extensively.  The  explanation  advanced  for  the  gypsum  will  also  account 
for  the  anhydrite,  and  this  will  be  given  in  "The  Gypsum  Masses." 

Genesis  of  the  Deposits 

The  preceding  pages  set  forth  the  problems  awaiting  solution,  and  only 
a  brief  recapitulation  is  deemed  necessary  of  some  of  the  most  significant 
facts  with  which  an  adequate  explanation  of  the  ore  genesis  must 
harmonize. 

The  association  of  the  ore  deposits  with  the  intrusives  is  interesting, 
and  a  study  of  the  lean  ores  is  one  that  promises  to  give  most  light  on  their 
origin.  Due  consideration  must  also  be  given  to  the  mechanical  alter- 
ation and  subsequent  changes  wrought  in  the  dike  materials  through 
which  suitable  solutions  passed,  and  by  which  the  concentration  and 
enrichment  of  the  ore  bodies  were  made  possible. 

The  fissures  produced  a  weakened  zone  which  not  only  permitted  the 
solutions  to  circulate,  but  determined  also  the  place  where  the  intrusives 
(dikes)  should  pass.  While  it  is  believed  that  chemical  alteration  has 
facilitated  important  surface  changes,  the  larger  structures  of  the  rock 
masses  in  depth  are  believed  to  have  been  caused  primarily  by  deep- 
seated  agents.  As  far  as  the  andesite  flows  are  concerned,  detailed  study 
shows  that  they  were  originally  almost  entirely  free  from  all  sulphides. 

The  limits  of  the  belt  which  suffered  shear  in  the  area  mapped  are  not 
definitely  known,  but  from  data  at  hand  it  appears  that  a  strip  which 
measures  1,000  ft.  or  more  in  width  and  several  miles  in  length,  at  least, 
has  been  affected.  This  zone,  which  deviates  locally,  trends  practically 
north  and  south  over  long  stretches,  and  it  is  characterized  from  point  to 
point  not  only  by  variation  in  width,  but  also  by  the  degree  of  mashing 
and  shearing. 

A  feature  of  economic  significance  and  one  that  should  receive  atten- 
tion is  the  fact  that  the  greatest  brecciated  and  comminuted  section  is  not 
symmetrically  located  with  reference  to  the  side  limits  of  the  shear  zone; 
but  is  decidedly  to  the  eastern  border  of  the  belt.  Thus  in  passing  across 
the  outcrop  of  the  belt  the  first  few  hundred  feet  encountered  closely 
resemble  schists,  while  toward  the  west  the  degree  of  schistosity  becomes 
less  and  less  until  finally  the  rock  masses  on  the  opposite  border  are  prac- 
tically free  from  such  induced  structures. 

Another  feature  which  is  very  conspicuous,  especially  in  Bully  hill, 
shows  that  locally  there  are  at  least  three  shear  zones  comprised  within  the 
belt.  Together  they  embrace  a  total  width  from  east  to  west  of  approxi- 

16  Bulletin  No.  430,  U.  S.  Geological  Survey,  p.  100  (1910). 


CALIFORNIA  95 

mately  1,000  ft.  They  are  seen  in  Fig.  6,  looking  northward,  as  a  series  of 
ridges  in  the  profile  of  the  hill.  The  eastern  zone  incloses  the  alaskite 
dike  and  contains  the  Delamar  lode  of  Bully  Hill. 

The  rough,  rugged  ridges  are  forms  which  have  resisted  erosion  more 
effectively  than  the  surrounding  materials.  With  the  exception  to  be 
noted,  all  such  ridges  are  referable  to  silicified  sheared  rock,  chiefly 
andesite  flows  and  tuffs.  It  appears  that  the  materials  are  mainly 
tuffaceous,  of  rather  wide  range  with  regard  to  fineness  of  grain;  and  it 
is  believed  that  such  materials,  because  of  their  porous  character,  per- 
mitted siliceous  waters  to  circulate  more  freely  than  the  more  massive 
andesite  flows.  The  solutions  came  from  below  and  are  believed  to  have 
transferred  silica,  which  was  derived  from  silicate  minerals  in  the  deeper 
parts  of  the  crushed  zone,  to  its  present  position.  Weathering  has  also 
influenced  the  composition  of  such  materials  by  dissolving  out  soluble 
constituents,  so  that  in  some  areas  the  mass  is  rather  porous. 

The  exception  referred  to  above  is  found  in  the  disconnected  masses  of 
alaskite-porphyry.  This  material,  because  of  its  position  and  external 
physical  appearance,  closely  resembles  the  masses  in  the  shear  zones. 
Close  inspection,  however,  shows  the  latter  to  contain  small  phenocrysts 
of  quartz,  while  the  former  contains  only  secondary  quartz.  In  some 
instances,  especially  where  shearing  has  been  excessive,  and  the  rock  is 
badly  stained  by  iron  oxide,  identification  can  be  established  only  by 
microscopic  study.  In  the  field  the  alaskite  is  often  mottled  with  darker 
patches,  and  in  most  instances  the  rock  breaks  with  conchoidal  fracture. 
These  serve  as  a  guide,  for  such  earmarks  are  never  seen  in  the  materials 
of  the  shear  zone. 

Attention  will  be  directed  first  to  relationships,  and  in  this  connection 
they  will  be  described  as  a  unit  and  will  embrace  the  following  elements: 
(1)  what  relation  exists  between  the  rhyolites  and  the  copper  ores;  (2) 
between  the  alaskite  and  the  copper  ores;  (3)  between  the  andesite  dike 
and  the  copper  ores;  (4)  and  lastly,  between  all  these  and  the  gypsum 
masses? 

(1).  The  most  important  changes  in  the  rhyolites  previous  to  miner- 
alization are  those  referable  to  mechanical  alterations.  The  rock  masses 
where  brittle  were  broken  and  a  zone  of  weakness  was  formed.  After 
long-continued  fracturing  the  intrusion  of  alaskite-porphyry  followed  the 
weakened  zone  and  was  accompanied  by  magmatic  emanations  which 
passed  along  the  borders  of  the  intrusive  and  were  otherwise  limited  to  the 
zone  of  mashing.  These  solutions  were  hot,  especially  rich  in  CO 2  at  the 
beginning,  and  later  they  carried  ore-bearing  and  silica  compounds.  It  is 
believed  also  that  these  richly  carbonated  waters  as  they  passed  through 
the  various  limy  strata  dissolved  large  amounts  of  lime  and  transported 
it  to  the  zone  where  vigorous  shattering  had  taken  place.  This  seems  in 
accord  with  the  facts,  as  the  veins  or  fissures  are  chiefly  filled  with  a  mix- 


96  BULLY   HILL   MINING   DISTRICT,    CALIFORNIA 

ture  of  calcite  inclosing  minor  amounts  of  chal  copy  rite  and  pyrite.  The 
fissured  rhyolites  were  thus  cemented  by  these  minerals. 

(2).  Long  before  the  alaskite  had  completely  solidified  stresses  again 
became  operative,  this  time  breaking  the  alaskite-porphyry  and  also 
disturbing  the  andesites.  Mineralization  and  impregnation  of  this  rock 
by  metallic  sulphides  resulted  It  is  therefore  logical  to  make  the  state- 
ment that  this  is  the  first  stage  in  the  genesis  of  the  copper  ores.  Accom- 
panying this  change,  although  not  definitely  connected  with  the  deposi- 
tion of  the  ores,  was  more  or  less  sericitization,  silicification,  etc.,  in  the 
rock  masses. 

The  brecciation  forces  which  acted  on  the  alaskite-porphyry  finally 
produced  essentially  the  same  shear  planes  that  were  observed  in  the 
inclosing  andesites,  so  that  both  rock  types  behaved  practically  as  a 
structural  unit  to  all  later  phenomena.  These  were  important  stages  in 
decomposing  the  constituent  minerals,  and  they  were  followed  by  chem- 
ical modifications  which  were  later  represented  by  completely  altered 
rock  masses  and  the  production  of  secondary  silicates. 

(3).  Shortly  after  the  production  of  the  foliated  structures  igneous 
activity  was  again  characterized  by  the  intrusion  of  an  andesite  dike, 
which  also  followed  the  foliation  planes,  and  in  places  cut  across  the 
alaskite-porphyry  by  intruding  into  the  shear  planes  developed  in  its 
mass.  Of  all  the  rocks  in  the  Bully  Hill  district  this  andesite  dike  was  the 
last  to  appear  and  it  closely  followed  the  alaskite-porphyry.  Outside  the 
area  mapped  an  intrusive  rock,  in  composition  more  basic  than  those 
described,  is  known.  From  these  relationships  it  is  believed  that  each 
fraction  from  the  original  magma  became  progressively  more  and  more 
basic,  and  that  accompanying  the  last  intrusion  magmatic  solutions  rich 
in  calcite  and  barite,  together  with  metalliferous  compounds,  were  also 
given  off  and  reached  the  sheared  zones.  These  solutions  started  out  hot 
and  in  their  upward  journey  they  received  heat  and  chemical  energy  from 
the  dikes  which  had  intruded  the  rocks  and  had  not  cooled  entirely. 
They  were  thus  effective  agents  and  at  once  attacked  the  rocks  which 
were  most  crushed  and  comminuted.  The  andesite  dike  in  places  was 
thus  encroached  upon  by  the  carbonated  compounds,  and  frequently 
entirely  replaced. 

Since  the  andesite  dike  is  partly  mineralized  it  follows  that  some  of  the 
economic  minerals  were  deposited  after  the  intrusion  of  the  alaskite-por- 
phyry. It  is  necessary  in  treating  the  genesis  of  the  ores  to  account  for 
the  copper  minerals  in  the  alaskite.  The  most  reasonable  and  logical  ex- 
planation is  that  they  were  transferred  by  the  agency  of  highly  heated 
solutions.  That  some  of  the  solutions  contained  lime  is  certain,  because 
in  the  andesite  dike  numerous  cavities  filled  with  calcite  exist. 

Copper  compounds  in  underground  highly  heated  solutions  are  doubt- 
less carried  in  many  forms,  probably  more  as  acid  compounds.  Assuming 


BULLY   HILL   MINING   DISTRICT,    CALIFORNIA  97 

that  pressure  and  temperature  are  important  factors  at  depth,  a  decrease 
in  either  of  these  might  furnish  conditions  under  which  deposition  would 
take  place.  Whatever  the  chemical  nature  of  the  solutions  that  trans- 
ported the  metallic  sulphides,  it  is  certain  that  they  were  deposited  in  the 
sheared  alaskite-porphyry  mass. 

The  magmatic  solutions  that  followed  the  andesite  dike  contributed 
additional  metallic  sulphides,  chief  of  which  were  blende,  bornite,  and 
galena.  Important  amounts  of  chalcopyrite  were  also  introduced  which 
greatly  added  to  the  richness  of  the  ores.  It  should  be  stated  that  in  all 
stages  of  mineralization  the  sheared  rocks  were  impregnated  indiscrimi- 
nately. The  element  of  control  seems  to  have  been  the  sheared  zone. 
In  several  places  the  andesite  dike  is  partly  mineralized,  but  so  far  as 
known  the  ores  appear  only  as  a  thin  crust  or  veneer  on  the  dike 
rock. 

Several  diamond-drill  holes  were  driven  through  the  andesite  dike  to 
ascertain  conditions  on  the  opposite  side.  No  ores  were  found,  and  so  far 
as  known  only  the  hanging-wall  side  of  the  dike  contains  sulphides.  In 
the  opinion  of  the  writer  the  opposite  side  of  the  dike  rock  should  be  pros- 
pected, although  it  is  quite  possible  that  the  position  of  the  dike  partly 
influenced  the  course  of  the  solutions  in  such  a  way  as  to  leave  the  rocks 
on  the  other  side  practically  barren.  So  far,  marketable  ores  have  been 
found  only  on  the  west  side  of  the  dike. 

It  is  not  believed  that  there  were  open  spaces  in  the  rocks  sufficiently 
extensive  to  account  for  the  ores  as  they  now  appear.  A  characteristic  of 
many  thin  sections  is  compactness  rather  than  porosity,  although  the  por- 
ous nature  of  the  tuffs  would  be  adequate  to  explain  ease  of  circulation  in 
any  direction.  The  interpretation  of  the  available  evidence  strongly 
supports  the  hypothesis  of  partial  to  complete  replacement,  and  the  facts 
upon  which  this  view  is  based  may  be  summarized  as  follows: 

(1).  The  lodes  preserve  structures,  especially  schistosity,  which  exist 
in  the  country  rock. 

(2).  Inclosed  masses  of  partly  replaced  remnants  of  the  original  crush- 
breccia  exist  as  cores. 

(3).  In  all  the  ore  associations,  there  is  clearly  to  be  seen  a  gradual 
transition  from  rich  through  lean  ore  to  barren  country  rock. 

The  elements  involved  in  the  explanation  are  consistent  with  the  facts 
and  the  hypothesis  of  replacement  molecule  by  molecule  of  the  rock 
masses  by  the  ores  seems  to  be  justified. 

In  connection  with  the  process  of  replacement,  it  is  of  interest  to  note 
how  a  very  acid  rock  like  alaskite,  and  for  that  matter  the  andesites  as 
well,  could  be  partly  if  not  wholly  replaced.  It  has  been  mentioned  that 
the  magmatic  waters  carried  carbon  dioxide  and  that  lime  was  dissolved 
from  strata  through  which  such  waters  passed.  Carbonated  waters,  as 


98 


BULLY   HILL   MINING    DISTRICT,    CALIFORNIA 


pointed  out  by  Clarke,17  are  solvents  for  most  of  the  common  minerals, 
including  quartz.  It  is  believed  that  some  of  the  solutions,  thus  carbon- 
ated, in  passing  through  the  disturbed  zone  attacked  the  acid  as  well  as 
the  basic  rocks  and  left  in  most  instances  only  the  resistant  minerals. 
Carbonate  was  in  this  way  introduced,  as  shown  in  Fig.  15.  It  was 
accompanied  in  some  instances  by  notable  amounts  of  chalcopyrite. 

Simultaneously  with  the  introduction  of  carbonate,  mineral  hydration 
and  removal  went  on,  and  in  some  rocks,  especially  the  dike,  considerable 


FIG    15. — FELDSPAR  IN  ANDESITE- PORPHYRY  BEING  REPLACED  BY  CALCITE. 
The  felty  areas  are  unaltered  ground  mass.     X  50  diameters.     Crossed  Nicols. 

chlorite  was  formed.  The  quartz  grains  of  the  alaskite-porphyry  were 
corroded,  and  in  some  instances  at  least  were  completely  removed.  The 
removal  of  quartz  is  believed  to  have  taken  place  through  the  influence  of 
the  alkaline  solutions.  This  phase  of  the  subject  will  receive  detailed 
discussion  under  a  later  heading. 

(4).  The  concordant  testimony  of  a  great  variety  of  evidence  from  a 
large  number  of  slides  suggests  several  important  phases  of  mineralization 


17  Bulletin  No.  491,  U.  S.  Geological  Survey,  p.  457  (1911). 


BULLY  HILL  MINING   DISTRICT,    CALIFORNIA  99 

processes.  The  study  shows  that  there  was  a  certain  definite  order  or 
sequence  of  deposition,  although  these  relations  are  partly  obscured  by 
the  deposition  of  some  compounds  which  began  with  the  earliest  stages 
and  continued  persistently  through  the  entire  process  to  the  last  stage. 
Such  minerals  as  pyrite  and  quartz  are  the  most  important  representa- 
tives of  this  class. 

The  important  phases  are  those  genetically  related  to  carbonatization 
and  sulphatization.  From  a  study  of  thin  sections,  the  former  was  a 
process  by  itself,  while  the  latter  included  pyritization  in  addition  to 
sulphatization. 

The  presence  of  certain  minerals  and  their  various  mutual  relation- 
ships suggest  a  common  source,  and  also  that  the  source  was  rich  in  the 
elements  which  form  the  compounds  now  found  in  the  rocks.  Carbon- 
ates, sulphates,  and  sulphides  are  seen  in  nearly  every  slide  in  varying 
amounts. 

The  most  important  geological  factor  which  assisted  the  circulating 
solutions  was  undoubtedly  the  sheared  structure  of  the  rock  masses. 
The  solvent  power  of  the  solutions,  under  high  temperature  and  pressure, 
was  very  great.  The  ferro-magnesian  minerals  were  the  first  to  be 
completely  altered,  and  these  changed  chiefly  to  chlorite.  The  feldspars 
apparently  were  the  next  to  yield,  and  alteration  has  gone  on  so  completely 
that  in  most  cases  very  little  remains  to  suggest  their  former  presence. 
In  some  of  the  ore  samples  grains  of  quartz,  supposed  to  be  the  original 
phenocrysts,  still  remain,  but  these  are  usually  badly  corroded.  Their 
relations  to  the  ores  are  shown  in  Fig.  14. 

VII.  THE  SULPHATE  DEPOSITS 

In  the  following  descriptions  of  the  various  types  of  sulphates,  the 
rocks  will  be  considered  in  order  of  their  abundance  as  they  have  been 
found  in  the  mine  workings  up  to  the  time  of  the  writing  of  this  paper. 
Whether  these  relationships  as  they  now  exist  will  continue  in  depth  is  a 
matter  on  which  we  have  no  absolute  data,  and  about  which  we  can  only 
speculate. 

The  sulphates  constitute  rocks  of  considerable  importance  in  the 
mines  of  this  district.  Their  existence  on  the  surface  with  the  exception 
of  barite  is  unknown,  and  their  extent  in  the  working  places,  although 
conspicuous,  is  not  usually  well  defined.  The  occurrence  of  sulphates 
underground  is  not  limited  to  the  upper  oxidized  zone,  but  these  com- 
pounds are  known  to  extend  as  low  as  the  1,000-ft.  level  (the  lowest  point 
reached  in  a  shaft  in  1912).  Although,  as  previously  stated,  there  are 
indefinite  areal  and  vertical  limits  to  the  occurrence  of  the  various  sul- 
phates, still  there  are  fragmentary  relationships  existing'  between  these 
compounds  and  the  rocks  which  serve  as  a  working  basis  for  interpreta- 
tion. The  principal  sulphates  are  gypsum,  anhydrite,  and  barite. 


100  BULLY   HILL   MINING    DISTRICT,    CALIFORNIA 

Gypsum 

The  monoclinic  hydrous  calcium  sulphate  (CaS042H20)  is  first  no- 
ticed in  the  mine  workings  near  the  300-ft.  level  and  from  this  point 
it  continues  downward  to  the  lowest  levels  of  the  mine.  It  is  usually  of 
a  light  gray  color,  massive  to  banded,  and  rarely  found  in  crystals.  Its 
banded  appearance  is  not  due  to  any  variation  in  its  composition  but  is 
produced  by  inclusions  of  other  rocks,  the  fragments  of  which  have  been 
arranged  by  shearing  processes  into  roughly  parallel  positions. 

At  some  points  it  is  found  in  larger  masses  in  a  comparatively  pure 
state,  but  the  greater  amount  in  the  drifts  and  tunnels  is  streaked  and 
locally  contains  pyrite.  The  larger  masses  are  soft,  usually  white  and 
everywhere  crystalline.  At  times  the  pure  fragments  are  translucent, 
and  it  is  possible  to  secure  masses  several  feet  in  dimensions.  Where  the 
rock  is  in  such  large  masses  it  is  very  difficult  to  mine  because  of  its  soft 
character  and  its  resistance  to  the  action  of  explosives.  For  this  reason, 
and  also  because  of  the  expense  of  drifting  through  it,  the  limits  of  such 
masses  are  not  known.  Drifts  in  such  bodies  are  characterized  by  being 
noticeably  dry. 

It  is  of  interest  to  note  that  the  gypsum  as  a  whole  is  found  limited  to 
the  shear  zone  in  depth,  and  thus  far  has  not  been  reported  from  any  point 
on  the  surface.  It  is  found  only  in  the  richest  mines,  intimately  associ- 
ated with  the  sheared  rocks.  In  a  general  way  it  is  seen  in  the  hand 
specimen  to  surround  masses  and  fragments  of  many  of  the  rocks  which 
enter  into  the  structure  of  the  hill. 

Anhydrite 

The  anhydrous  calcium  sulphate,  anhydrite  (CaS04),  is  found  in  the 
rocks  in  very  close  association  with  gypsum.  Like  gypsum,  it  has  never 
been  found  on  the  surface.  In  the  fresh  state  it  is  marble-like  in  texture 
and  varies  in  color  from  a  dull  white  to  various  shades  of  light  blue.  It 
is  never  translucent,  and  is  easily  distinguished  from  gypsum  in  being 
harder  and  in  having  a  pseudo-cubic  cleavage  in  which  the  planes 
are  perpendicular  to  each  other,  but  of  a  somewhat  differing  degree  of  per- 
fection. It  is  less  abundant  than  gypsum  and  optically  differs  from  it  in 
having  moderate  relief  and  high  double  refraction.  The  rectangular 
cleavage  is  also  marked.  In  thin  section  it  is  seen  to  have  practically  the 
same  relationships  as  the  gypsum. 

Barite 

Barite,  the  orthorhombic  sulphate  of  barium,  BaSC>4,  occurs  only  spar- 
ingly in  the  mines  of  the  district.  It  is  a  heavy  light-colored  mineral 


BULLY   HILL   MINING   DISTRICT,    CALIFORNIA  101 

having  vitreous  luster.  This  mineral  is  the  only  sulphate  found  on  the 
surface  and  is  usually  detected  by  its  glistening  crystal  faces  and  the  rela- 
tively great  weight.  According  to  Diller18  the  barium  had  its  source  in 
the  feldspars  of  the  alaskite-porphyry.  After  a  number  of^careful  tests 
the  writer  was  unable  to  detect  any  barium  in  the  feldspars  of  this  dike 
rock.  It  is  believed  that  the  barium  which  furnished  the  barite  had  its 
origin  in  the  same  source  which  supplied  the  sulphides.  Since  this  mineral 
is  so  sparingly  present  it  will  not  receive  further  discussion. 

Origin  of  the  Deposits,  with  Special  Reference  to  Gypsum 

Before  proceeding  to  a  discussion  of  this  subject  a  summary  of  the 
relationships  of  the  gypsum  is  given.  An  effort  has  been  made  to  bring 
together  all  the  data  bearing  directly  on  the  problem  and  also  to  condense, 
as  far  as  possible,  the  descriptions  of  numerous  slides  examined.  The 
statements  represent  facts  gathered  from  the  field  as  well  as  from  detailed 
microscopic  study.  A  few  of  the  most  important  relationships  are  given 
below : 
Field  occurrences  of  gypsum : 

1.  It  is  found  only  in  the  greatest  shear  zones. 

2.  It  is  never  found  on  the  surface  in  the  vicinity  of  the  mines. 

3.  It  begins  on  the  300-ft.  level  of  the  mine  and  extends  to  the  low- 
est (1,000-ft.)  level. 

4.  It  does  not  occur  outside  the  zone  affected  by  shear. 
Microscopic  relations: 

1.  It  replaces  quartz  grains  and  glass  fragments. 

2.  It  occurs  as  fissure  fillings. 

3.  It  is  an  alteration  product  after  anhydrite. 

4.  It  completely  surrounds  rock  fragments. 

5.  It  is  intimately  associated  with  the  sulphides. 

In  order  to  explain  the  conditions  given  and  to  account  for  the  origin 
of  the  gypsum  in  this  deposit,  it  will  be  well  first  to  outline  the  different 
theories  advanced  for  the  accumulation  of  gypsum  the  world  over.  These 
are:  First,  deposition  from  sea  water.  Second,  deposition  through  vol- 
canic agencies.  Third,  deposition  by  thermal  springs.  Fourth,  depo- 
sition through  the  action  of  sulphuric  acid,  derived  from  pyrites,  upon  the 
carbonate  of  lime.  Fifth,  Hunt's19  chemical  theory  of  gypsum  formation. 
This  theory  is  somewhat  complex,  but  Hunt  believed  it  applied  to  a  large 
part  of  the  gypsum  of  marine  and  fresh-water  origin.  This  theory  does 
not  apply  in  this  case. 

Applying  these  criteria  to  the  deposit  in  this  district  we  find  that  the 

18  Redding  Folio,  No.  138,  U.  S.  Geological  Survey,  p.  12  (1906). 

19  Quarterly  Journal  of  the  Geological  Society,  vol.  xvi,  p.  154  (1860);  Chemical  and 
Geological  Essays,  pp.  80  to  92  (1874). 

10 


102  BULLY   HILL   MINING   DISTRICT,    CALIFORNIA 

mode  of  formation  as  set  forth  by  the  first  and  fifth  theories  is  not  appli- 
cable. The  second  and  fourth  only  demand  careful  consideration,  and  for 
convenience  of  discussion  will  be  taken  up  in  the  reverse  order. 

Deposition  through  the  Action  of  Pyrites  upon  Carbonate  of  Lime. — - 
This  method  is  perfectly  possible  and  has  taken  place  without  doubt  in  an 
extensive  way  in  nature,  but  there  are  certain  initial  conditions  which  do 
not  appear  in  this  region.  First  of  all  there  must  be  deposits  of  limestone 
sufficiently  large  to  form  the  gypsum  deposit  as  it  now  appears.  That 
sulphides  oxidize  to  sulphates  is  well  known.  If  we  start  with  pyrite  the 
final  oxidation  products  are  indicated  by  the  following  chemical  equation : 

FeS2  +  70  +  H20  =  FeS04  +  H2S04. 

It  is  seen  that  one  molecule  of  pyrite  will  yield  one  each  of  FeSO4  and 
H2S04.  To  be  on  the  safe  side,  it  is  assumed  that  both  FeS04  and  H2S04 
operate  to  produce  sulphate  of  lime,  although  it  is  very  doubtful  if  the 
ferrous  sulphate  acts  in  this  manner.  The  molecular  weight  of  gypsum 
is  172  while  that  of  pyrite  is  120.  If  these  be  converted  into  molecular 
volumes  it  is  found  that  for  74.8  volumes  of  gypsum  we  require  24  vol- 
umes of  pyrite,  or  that  for  every  100  volumes  of  gypsum  there  must  be  32 
volumes  of  pyrite,  on  the  basis  that  H2S04  only  goes  to  make  up  the  sul- 
phate, Under  these  conditions,  and  also  assuming  that  the  gypsum  in 
territory  not  yet  explored  is  as  thick  as  that  already  found,  a  uniform  bed 
of  pyrite  approximately  224  ft.  thick  would  be  required.  If,  however, 
both  FeS04  and  H2S04  go  to  form  the  sulphate,  then  one-half  of  this 
thickness  would  suffice.  There  is  no  evidence  that  any  such  deposit  of 
pyrite  ever  existed  in  the  district. 

By  the  same  method  of  reasoning  it  is  found  that  to  account  for  the 
calcium  in  the  gypsum  a  bed  of  carbonate  approximately  350  ft.  thick 
would  be  required.  There  is  no  evidence  that  any  such  bed  of  car- 
bonate ever  existed  in  the  mine  workings.  On  the  other  hand,  there  is 
distinct  proof  that  clastic  volcanic  rocks,  or  their  remnants,  are  the  dom- 
inant rocks  of  the  district.  The  failure  of  this  theory  to  explain  the  de- 
posits makes  it  evident  that  this  method  of  origin  could  not  have  been  the 
one  to  which  this  deposit  owes  its  existence. 

Deposition  from  Thermal  Springs,  and  Through  Volcanic  Agencies. — 
These  two  theories  have  been  grouped  as  one,  since  their  effects  from  a 
geological  point  of  view  are  very  similar.  It  is  well  known  that  emana- 
tions from  deep-seated  cooling  igneous  magmas  are  numerous,  and,  as 
shown  in  an  important  paper  by  Lincoln,20  consist  of  acids,  gases,  and 
sublimates. 

By  referring  to  the  structural  section,  Fig.  1,  it  will  be  seen  that  a 
massive  limestone  (the  McCloud)  has  been  involved  in  the  folded  and 
otherwise  compressed  strata.  Since  this  limy  member  was  in  the  crush 

10  Economic  Geology,  vol.  ii,  No.  3,  p.  258  (Apr.-May,  1907). 


BULLY   HILL   MINING   DISTRICT,    CALIFORNIA  103 

zone  through  which  the  emissions  of  the  igneous  magma  passed,  it  is  per- 
fectly reasonable  that  the  rock  would  suffer  more  or  less  solution  by  the 
acid  liquid  solutions.  These  may  have  been  in  part  water  containing 
C02,  SO2,  SO3,  or  S04.  Any  of  these  alone  would  dissolve  the  lime  car- 
bonate and  transport  large  amounts  to  higher  points.  Whether  the  lime 
was  carried  as  carbonate  or  sulphate  or  as  a  mixture  of  the  two  is  a  matter 
about  which  we  can  only  speculate.  It  is  possible  that  certain  solutions 
were  chiefly  carbonate  while  others  were  sulphate  in  general  composition. 
That  both  solutions  existed  is  shown  by  the  presence  of  carbonate  as  well 
as  sulphate  in  the  rocks,  but  since  sulphate  is  in  largest  amount  it  follows 
that  solutions  of  this  character  were  dominant. 

Whether  the  sulphate  was  deposited  as  anhydrite  or  as  gypsum  is  not 
certain,  although  Graton21  from  his  studies  concludes  that  anhydrite  is 
primary  and  that  gypsum  is  a  secondary  product  derived  from  anhydrite. 
There  is  room  for  further  study  on  this  point  because  of  the  well-known 
fact  that  gypsum  may  be  transformed  into  anhydrite,22  or  that  the  re- 
verse reaction,  anhydrite  into  gypsum,  may  readily  take  place.  Further- 
more, it  is  known  that  anhydrite  thus  formed  may  be  reconverted  into 
gypsum.23 

The  writer  is  fully  aware,  however,  that  within  the  limits  of  experi- 
ment the  solubility  of  sulphate  increases  up  to  about  38°  C.  and  then  de- 
creases for  additional  increments  of  temperature.  This  is  somewhat 
against  the  theory  of  transportation  of  sulphate,  but  there  are  so  many 
variable  factors  which  tend  to  offset  this  decrease  in  solubility  that  we  are 
driven  to  the  conclusion  that  these  sulphate  deposits  have  accumulated  by 
the  transportation  of  lime  by  magmatic  solutions  from  deep-seated  sources. 

Considering  the  origin  of  the  gypsum  deposit  as  well  as  that  of  the 
metallic  minerals  so  closely  associated  with  it,  this  theory  seems  to  accord 
most  satisfactorily  with  all  the  fundamental  relations  and  facts  brought  out 
by  detailed  study. 

VIII.     SUMMARY 

From  the  previous  descriptions  and  discussions,  and  also  from  a  de- 
tailed study  of  all  available  data  bearing  directly  upon  the  deposits  of  this 
character,  the  following  general  conclusions  seem  to  be  warranted: 
1.     The  structure  is  conspicuously  closely  crumpled,  and  where  slightly 
overturned  the  folds  are  accompanied  by  breaks  which  result  in  a 
tendency  to  develop  weak  crush  and  shear  zones  along  the  chief 
planes  of  movement. 

.    ^Bulletin  No.  430,  U.  S.  Geological  Survey,  p.  100  (1910). 

22  American  Chemical  Journal,  vol.  xi,  p.  31  (1889). 

23  F.  Hammerschmidt:  Miner -alogische  and  Petrographische  Mittheilungen,  vol.  v, 
p.  272  (1882-83). 


104  BULLY   HILL   MINING   DISTRICT,    CALIFORNIA 

2.  The  copper  ores  of  the  Bully  Hill  district  were  originally  deposited 
from  magmatic  solutions  in  which  the  metals  were  transported  as 
soluble  sulphides  and  were  deposited  as  such. 

3.  From  the  character  of  the  metallic  sulphides,  the  associated  minerals, 
and  the  structural  relationships,  it  appears  that  replacement  has  been 
the  dominant  process  in  these  deposits. 

4.  The  accumulation  and  concentration  of  the  ores  as  they  are  now 
found  involves  secondary  enrichment,  changes  in  which  precipita- 
tion by  mingling  solutions  and  reactions  on  wall  rock  are  of  greatest 
importance. 

5.  The  mineralization  processes  have  apparently  taken  place  under 
conditions  which  were  entirely  independent  of  rock  mass  control,  as 
tuffs,  flows,  and  dikes,  differing  widely  in  physical  and  chemical  make 
up,  are  indiscriminately  replaced. 

6.  The  lime  as  calcite,  and  the  sulphate  either  as  anhydrite  or  gypsum, 
had  an  origin  in  deep-seated  sources,  and  both  these  minerals  were 
genetically  related  to  the  sulphidation  process  which  has  given  rise  to 
the  ores. 

IX.  BIBLIOGRAPHY 
Geology  of  Shasta  County,  Cal. 

DILLER,  J.  S.:  Folio  No.  138,  U.  S.  Geological  Survey  (1906). 

FAIRBANKS,  H.  W.:  Geology  and  Mineralogy  of  Shasta  County,  Cal.,  Eleventh  Report, 

California  State  Mineralogist,  pp.  24-53  (1892). 
Notes  on  Some  Localities  of  Mesozoic  and  Paleozoic  in  Shasta  County,  Cal., 

American  Geologist,  vol.  xiv,  pp.  25-31  (1894);  Describes  geologic  structure. 
Outline  of  the  Geology  of  California  with  Reference  to  its  Mineral  Deposits, 

Mining  and  Scientific  Press,  vol.  Ixxiv,  pp.  132-232  (1897). 
SMITH,  J.  P.:    Salient  Events  in  the  Geologic  History  of  California,  Science,  N.  S., 

vol.  xxx,  pp.  346-350  (1909).     Outlines  the  geologic  history  from  the  Cambrian 

to  the  present. 

Ore  Deposits  of  Shasta  County,  Cal. 

BECK,  Dr.  R.:  The  Nature  of  Ore  Deposits.  Translated  by  W.  H.  Weed.  487  pp. 
(New  York,  1909). 

DILLER,  J.  S.:  Folio  No.  138,  U.  S.  Geological  Survey  (1906). 

FAIRBANKS,  H.  W. :  Geology  and  Mineralogy  of  Shasta  County,  Cal.,  Eleventh  Report, 
California  State  Mineralogist  (1892). 

GRATON,  L.  C.:  Contributions  to  Economic  Geology,  Bulletin  No.  430,  U.  S.  Geo- 
logical Survey,  pp.  71-111  (1910). 

HERSHEY,  OSCAR  H. :  Primary  Chalcocite  in  Calif ornia,  Mining  and  Scientific  Press, 
vol.  xcvi,  pp.  429-430  (1908). 

PACKARD,  GEORGE  A.:  Copper  Mines  and  Smelteries  of  Shasta  County,  Cal.,  Engi- 
neering and  Mining  Journal,  vol.  Ixxxviii,  pp.  393-399  (1909). 

THOMAS,  H.  H.  and  MACALISTER,  D.  A. :  The  Geology  of  Ore  Deposits,  pp.  160-161 
(London,  1909). 


BULLY   HILL   MINING   DISTRICT,    CALIFORNIA  105 

Gypsum 

Formation  of  Gypsum,  Quarterly  Journal  of  the  Geological  Society,  vol.  v,  pp.  172-173, 

339;  vol.  vi,  p.  xlix,  (1849,  1850). 
HUNT,  T.  STERRY:   On  the  Origin  of  Gypsum,  Chemical  and  Geological  Essays,  chap. 

8  (1874). 
ROSE,  H.:     On  the  Solubility  of  Gypsum,  Poggendorfs  Annalen,  vol.  xciii,  p.  606 

(1854). 
MARIGNAC,  C.:  On  Solubility  of  Gypsum,  Annales  de  Chimie,  5th  ser.,  vol.  i,  p.  274 

(1874). 
MCCALEB  :   On  the  Solubility  of  Gypsum,  American  Chemical  Journal,  vol.  xi,  p.  31 

(1889). 
ROGERS,  A.  F.:    The  Occurrence  of  Gypsum  and  Anhydrite  at  the  Ludwig  Mine,. 

Lyon  County,  Nevada,  Economic  Geology,  vol.  vii,  pp.  185-189  (1912). 
SURR,  GORDON:    Notes  on  Occurrence,  Origin,  etc.,  of  Gypsum,  Mining  World,  vol. 

xxxiv,  pp.  1283-1284  (1911). 
HESS,  F.  L. :    A  Reconnaissance  of  the  Gypsum  Deposits  of  California,  Bulletin  No. 

413,  U.  S.  Geological  Survey  (1910). 

Miscellaneous 

CLARKE,  F.  W.:  The  Data  of  Geochemistry,  Bulletin.  No.  491,  U.  S.  Geological  Survey 
(1911). 

GEIKIE,  JAMES:   Structural  and  Field  Geology  (New  York,  1905). 

BARKER,  ALFRED:    The  Natural  History  of  Igneous  Rocks  (New  York,  1909).    • 

IDDINGS,  J.  P.:    Igneous  Rocks  (New  York,  1909). 

•KEMP,  JAMES  F. :  Secondary  Enrichment  in  Ore-Deposits  of  Copper,  Economic  Geol- 
ogy, vol.  i,  pp.  11-25  (1906). 

LINCOLN,  F.  C.:  Magmatic  Emanations,  Economic  Geology,  vol.  ii,  pp.  258-274  (1907). 

POSEPNY,  FRANZ:   The  Genesis  of  Ore  Deposits,  2d  ed.  (New  York,  1902). 

READ,  T.  T.:  The  Secondary  Enrichment  of  Copper-Iron  Sulphides,  Transactions 
of  the  American  Institute  of  Mining  Engineers,  vol.  xxxvii,  pp.  297,  895  (1906). 

RICKARD,  T.  A'.:    Ore  Deposits — A  Discussion.     (New  York,  1905). 

SULLIVAN,  EUGENE  C. :  The  Chemistry  of  Ore-Deposition — Precipitation  of  Copper 
by  Natural  Silicates,  Economic  Geology,  vol.  i,  pp.  67-73  (1906). 

WEED,  W.  H.:  The  Copper  Mines  of  the  World,  pp.  297-302  (New  York,  1907). 

WINCHELL,  A.  N.:  The  Oxidation  of  Pyrite,  Economic  Geology,  vol.  ii,  pp.  290-294, 
(1907). 


VITA 

ALBERT  CLARENCE  BOYLE,  Jr.  (Salt  Lake  City,  1879) 

B.S.,  E.M.,  Utah  School  of  Mines,  1906 

A.M.,  Columbia  University,  1910 

Instructor,  School  of  Mines,  Utah,  1903  to  1907;  Assistant 
in  Geology,  Columbia  University,  1907  to  1910;  Professor 
of  Mining,  Metallurgy  and  Geology,  University  of 
Wyoming,  1910  to  date. 


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